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I agree this isn't as big of a deal as the stockmarket may imply, but this line bothers me: "That equates to 1 vehicle fire for every 20 million miles driven,

I agree this isn't as big of a deal as the stockmarket may imply, but this line bothers me: "That equates to 1 vehicle fire for every 20 million miles driven, compared to 1 fire in over 100 million miles for Tesla. This means you are 5 times more likely to experience a fire in a conventional gasoline car than a Tesla!" Americans drive an aggregate of 3 trillion miles every year, while Tesla drivers have done 100 million (and they don't cite this number; are they including test drives?). That's well over an order of magnitude difference. Plus, the average Tesla driver is currently probably a superior driver (if for no other reason than they have a brand new expensive car) and has taken better care of their car (since it's within 2-3 years old, tops). In theory, Teslas will eventually become more mainstream over the years -- resold, price drops, lower-end models, etc. Again, I don't think their conclusion about Teslas being safer overall is wrong. However, their conclusion of the likelihood of a Tesla catching on fire seems off, and the exclamation mark makes this press release seem glib.

squidi 13y ago
> Americans drive an aggregate of 3 trillion miles, while Tesla drivers have done 100 million. That's well over an order of magnitude difference. The data on 100 million is probably enough to compare with the 3 trillion miles. The populations don't need to be equal to compare them, just big enough that they are random and distributed enough.
- nonchalance 13y ago
  To put it in perspective, the disparity is equivalent to polling 10K americans and extrapolating to all of america (which, for better or for worse, is what most pollsters do).
  - ProCynic 13y ago
    If the sample is truly random, it doesn't matter what the population size is. Of course, truly random samples are hard to get.
    - adw 13y ago
      That depends on the population variance.
    - deleted 13y ago
      [deleted]
  - akavi 13y ago
    Except pollsters put in a lot of effort in making sure that the sample is representative of the larger population. Which is not true here, as the GP correctly notes.
    - mikeash 13y ago
      Do they really? My only interaction with pollsters has been either having them call me or solicit me on the street, and both approaches have a tremendous inherent bias. As far as I know, this is how the big national agencies do things.
      - PeterisP 13y ago
        There are all kinds of adjustments done afterwards to correct for various factors. For example, you know the age distributions in USA; and if you find out your phone calls are getting twice as many seniors than the proportion should be[1], then you throw away a random parts of them so that they don't skew final 'data' towards the typical opinions of seniors. [1] Assuming that you're not measuring average age or measuring 'who is at home', but if you want to see, say, the average political opinion of total USA population, which tends to correlate with age.
        mikeash 13y ago
        It still seems impossible to correct for everything. Sure, you could correct for age as you describe, but I imagine that landline phone ownership correlates with political opinions in all sorts of other ways too. Furthermore, how do you gather the data needed to correct the polling numbers without being able to accurately poll people in the first place? Seems like a complete chicken-and-egg problem.
        PeterisP 13y ago
        "how do you gather the data needed to correct the polling numbers" -> you use the census. You need some info about the total population, you get it periodically and it doesn't change that much; you don't need to repeat it for every survey.
  - Zikes 13y ago
    I often see polls of 1K Americans and extrapolating out from there. An example: http://www.webpronews.com/americans-think-cloud-computing-comes-from-actual-clouds-2012-08 http://www.webpronews.com/americans-think-cloud-computing-co... Of course, the refrain I often hear is that as long as you pick the RIGHT 1,000 Americans, it's as good as polling all 319 million.
    - gnaritas 13y ago
      > Of course, the refrain I often hear is that as long as you pick the RIGHT 1,000 Americans, it's as good as polling all 319 million. If it's a proper random sample, then it's far better than sampling all 319 million because it's 95% accurate with about a 3% margin of error and vastly cheaper and actually practical; you can't poll 319 million people.
  - mikeash 13y ago
    It's counterintuitive, but the sample size needed for a good measurement doesn't much depend on the size of the overall population. What matters is getting a properly random sample. This is where pollsters fall down, because their "random" sample tends to be heavily biased toward the sort of person who has a landline telephone and doesn't hang up on pollsters. Polling 10,000 Americans would be vast overkill, in any case.
  - deleted 13y ago
    [deleted]
  - gnaritas 13y ago
    You say that as if 10k is too small a sample size to extrapolate accurately with, but actually that's a huge sample size that if done properly would be extremely accurate. You don't need to poll anywhere near 10k people to accurately predict all Americans views. You can sample less than 2000 people and get 99% accuracy with a 3% margin of error for a population of 325 million. Increasing the sample size to 10k simply reduces the margin of error to 1.29%, hardly worth the extra sampling of 8k people.
  - auctiontheory 13y ago
    If you haven't read Asimov's Election Day, I highly recommend it.
- broostoryco 13y ago
  We are comparing tail events with low probabilities.
- gkoberger 13y ago
  When trying to get popular opinion for, say, an election -- sure. However, there was one fire over 100 million miles. The problem isn't the 100 million, it's the 1 fire. This wasn't a controlled experiment, either -- they just stopped the clock as soon as the first fire happened, and multiplied. A week ago, they could have said "You have exactly a 0% chance of your Tesla catching on fire" and have been right by this logic. To think of it another way -- let's say you get lucky and get a hole-in-one your 10th time golfing. Does that mean you'll have 10 hole-in-ones if you golf 100 times? Doubtful. EDIT: Also, don't forget that Elon is mixing numbers. There's no fire if someone doesn't run over something. All these numbers show is that the average driver is more likely to run over something. Of course Tesla drivers run over fewer things -- there are no 16 year old kids texting while driving a Tesla... yet.
  - revelation 13y ago
    Doesn't stopping the clock after 1 fire just penalize them, not benefit them? That said, I also think the 1 fire is the problem here. Just think about how that relation changes with 2 fires.
    - jamesaguilar 13y ago
      It probably penalizes them, assuming the no-fires-for-100m-miles was not a fluke. There's no way to know for sure without knowing the true distribution of fires per mile.
    - BWStearns 13y ago
      The chance goes from 0.000000010 to 0.000000020 If I had the cash I would still purchase a Tesla after the second fire as well.
      - sgustard 13y ago
        Thanks for converting that to "fires per mile".
      - moocowduckquack 13y ago
- thedufer 13y ago
  The relevant metric here seems to be 'miles between fire events'. On this metric, we have exactly 1 data point for Tesla. I would hardly call that "probably enough". Of course, I'm exaggerating in the other direction. What we really should be calculating is the odds that Teslas burst into flames less often than the average car, given that the average car does so every 20 million miles and the first such event in a Tesla was at the 100 million-mile mark. We're still failing to account for the fact that the average Tesla is newer and probably better-kept than the average car, but it would at least be a reasonable start. I don't know enough statistics to perform this calculation, but I would like to see how it is done.
  - jurjenh 13y ago
    An easy starting point would be to get this kind of data on similarly aged cars - cars sold over the last 2-3 years, then see what stats you can get there. I'd guess that you'd find some models that have never caught fire and some that have done so a lot more than tesla's, but that's pure speculation on my part.
  - PeterisP 13y ago
    We have enough events, because in this case it is appropriate to model the actual random event as 'million miles driven' with a chance of fire happening or not happening. Gasoline cars have a mean of 0.05 fires per million miles, and given the current Tesla data, the mean is 0.01 fires per million miles. I'm not taking out a calculator, but it would come out to an extremely low (0.0001%) the 'true' fire chance is the 0.05 gas car rate or higher; the 95% confidence interval should be 0.01 +- 0.02 or tighter, so still twice better than gas cars. For an exaggerated example, if Tesla had driven a billion miles and had 0 fires, you shouldn't say that there's not enough data - you definitely would have enough data to say that the chance of fire is below the gas-car rate of 5 fires per 100 million miles.
    - thedufer 13y ago
      Why is million miles driven a better way to model it than billion miles driven, for example? If you happen to choose that, there clearly isn't anywhere near enough data. I'm honestly curious how one models this type of thing statistically, and I am not convinced enough of its obviousness to just accept numbers that someone throws around.
grinich 13y ago
Hard to argue against Elon's last sentence, though.
- deletes 13y ago
  That should be the main point of his argument, instead of speculative statistics.
ececconi 13y ago
I agree, the exclamation mark was a terrible thing to include. Imagine if someone died, would they still put the exclamation mark there?
sologoub 13y ago
The page is as much about marketing (maybe more) as it is about safety or the incident. Especially, after the stock dropped, can you blame them? That said, I'm not really sure why this is such big news. Accident happened due to debris on the road. No one was hurt. The car was severely damaged, but got the owner to safety. AND THEN a small fire happened... Then I read things like this: http://www.dailynews.com/general-news/20130928/5-killed-1-injured-in-fiery-single-vehicle-crash-in-burbank http://www.dailynews.com/general-news/20130928/5-killed-1-in... Let's consider this for a second - Tesla Model S had a no-injury accident and made national news. 5 kids burned alive in a Sentra, and this barely stayed on local news for 3 days. Tesla Model S is a phenomenal vehicle with an excellent, if short-ish, track record. It really annoys me that reporters go out of their way for sensationalist articles, when there are far worse tragedies to cover.
- baddox 13y ago
  > The page is as much about marketing (maybe more) as it is about safety or the incident. What does that mean? Taking a common definition of "marketing" to be "expressing the value of a product to potential customers," any article that is about safety or about a recent product incident is also marketing. It sounds like you're using "marketing" as an ill-defined term that basically just means "something bad about the way a company publishes information."
  - sologoub 13y ago
    "Bad" is subjective, when I personally think Marketing, I mean putting a spin on things and presenting it in a more favorable light for the company. This is not a dry facts page, but a public relations communication that is intended to sell you on the fact that Tesla Model S is a safe vehicle. Nothing wrong with that and nothing "bad" as you seemed to imply.
    - baddox 13y ago
      But all of the claimed facts are either true or false, right?
danso 13y ago
I agree...The kind of driver who can buy a Tesla is likely the kind of driver who has acquired enough education and comfortable wealth to be a competent driver (on the average). Moreover, there's survivor bias here: If you've made it far enough in life to buy a Tesla, you're probably a person with pretty decent habits. And finally, if you've bought an expensive car like the Tesla, you may be more likely to drive it more carefully than the average person does their Honda Accord. I don't think Musk is any more dishonest than any other CEO, and he's probably more honest, by far, on average. However, it kind of pains me to see how easy it is for him to sway the hacker crowd with data-interpretations that would be questionable by any standard. If this is among the strongest empirical evidence he can provide, then I think we should maintain some skepticism.
- alxp 13y ago
  A study by UC Berkeley and the University of Toronto actually showed that luxury car owners were by far the most aggressive drivers, and the least likely to stop for other road users. http://www.bankrate.com/financing/cars/study-bmw-drivers-are-the-worst/ http://www.bankrate.com/financing/cars/study-bmw-drivers-are... For whatever reason BMW stood out most of all as the worst of the worst in this study, but 'expensive car drivers are better drivers' has been proven to not be an assertion you can make from common sense or intuition.
  - danso 13y ago
    Without reading the study, I'm ready to agree that its conclusions are correct. But I'd argue we're still comparing apples to oranges here: 1. We can't assume that Tesla drivers are the same as traditional luxury car drivers. While cars are a statement of wealth, and many arrogant bastards like making that statement...A Tesla is ostensibly a statement of a few other things, such as concern for the environment, optimism about technology, etc. etc...in the same way, even though many programmers make high-end salaries (low-6 figures), I wouldn't say that we can expect these programmers to golf as much as the average non-programmer low-6-figure-earner. 2. Reading the link you posted, it said the study evaluated based on the frequency of accidents and the size of payout...I couldn't find the study on the website, but this statement from the article was ambiguous to me: > According to data from IIHS website, the collision insurance losses on BMW 7 Series are more than twice the average for vehicles nationwide, and BMW 3 Series two-doors are more than three times. Twice the average of what...? Payouts total? Payouts per claim? Payouts per claim normalized by number of total cars of that kind on the road? 3. The NHTS data concerns the number of fires. For the study you cited to be more relevant, we'd have to know what proportion of the insurance claims also involve vehicle fires. If you're thinking, "Well, if a car caught on fire, then that's likely because of an accident...so more accidents mean more fires"...well, a> That's a classic logical fallacy (All dogs are animals. Sara owns a lot of animals. Therefore, Sara owns a lot of dogs) and b> the kinds of accidents that make up a majority of insurance claims (my guess is low-to-medium speed fender benders) may not represent a significant portion of incidents that end up in a flaming wreck. All in all, I wouldn't say that Musk is clearly wrong here...He could be right, we just don't have enough information either way...so it feels slightly dirty -- a slap in the face of analytical thinking -- for him to cite these statistics as being anywhere near conclusive.
sz4kerto 13y ago
> I agree this isn't as big of a deal as the stockmarket may imply I firmly believe that what's happening on the stockmarket and the fire are merely a coincidence, there isn't a causal relation between them. Tesla stock has been due to correct back for a while, and a downgrade came in as well (unrelated to the fire). Edit: first rule of the HN club: only positive things about Tesla, otherwise you are going to be voted down. Neutral opinion is considered negative. :)
eridius 13y ago
> Plus, the average Tesla driver is currently probably a superior driver I can play the conjecture game too. The average Tesla driver is probably a worse driver than the average gas-powered car driver. Why? Because they have the disposable income to purchase a Tesla, which means they're probably less careful with their possessions (as they can presumably afford to replace them), plus the Model S is a sports car so they're probably driving faster and more carefree than your average person. Not that I really believe this, but come on, your argument is completely made up.
- SEJeff 13y ago
  I would counter with, "How dare you assume that all Tesla drivers have disposable income to throw around". I happen to be close to buying one and know a few other owners who are average middleish class people who normally would have bought a porsche or a tesla. I work in tech and as a result am paid pretty decent. Do I have disposable money (or my friends) to buy a Tesla Model S? No! However, given where I live and where I want to drive + the recharging stations, Tesla is a good option for me. Do not assume just because someone is able to get enough money to buy something expensive,that they have tons of money. By that same logic, anyone who is able to buy a home is clearly flush with cash and able to throw it all around. Completely ridiculous.
  - dandelany 13y ago
    You're missing the point - he's not actually making that argument, he's showing how easy it is to make any argument if you back it up with anecdotal conjecture rather than data.
    - eridius 13y ago
      Exactly. I rather suspect that Tesla drivers are actually comparable to other drivers, rather than being demonstrably better or worse, but the only way to know would be to actually conduct a study on the subject.
      - 13y ago
larrys 13y ago
"they have a brand new expensive car" A good point. It would be interesting to compare the miles drive on "brand new expensive cars" not just all cars which include obviously older and/or poorly maintained vehicles.
- baddox 13y ago
  Why would that be relevant? Anyone who buys a Tesla Model S will instantly be in the category of "people who buy brand new expensive cars," so the Model S stats are sufficient.
  - kschults 13y ago
    That's the point. larrys wants to compare the Model S miles driven by "people who buy brand new expensive cars" against other car miles driven by "people who buy brand new expensive cars," instead of comparing the Model S miles [...] against other car miles driven by everyone.
codex 13y ago
This comparison is a bit off. Most of the cars which catch fire are old. The comparison should be to a similarly priced, brand new luxury car. Very few of those catch fire, either.
- bborud 13y ago
  Well, then I would limit it to Ferraris that are 3 years or younger :).
jusben1369 13y ago
I think this is Elon's one blind spot. For a engineer he's awfully "salesy" at times. The whole lease thing was really distasteful. This less so; but still a bit awkward. Why not just end with "Fires are unfortunately a risk for electric and gasoline cars. Each year in the US there are more than 150,000 fires. As more and more Tesla's enter the world we're going to experience all manner of events" That would be the right way to put this in context. However, I suspect that to overcome the naysayers and truly change a market (electric cars) requires an almost insane love for what you do - which makes you sound a little too defensive when something goes wrong.
- _delirium 13y ago
  I have no idea how Tesla operates internally, but I wouldn't be too surprised if, like at most companies, letters that go out under the CEO's name are vetted by both the legal and PR departments, and possibly written or edited by them. If that's the case, then "Elon Musk" is a sort of composite entity, which includes a human named "Elon Musk", but not solely that human.
  - jusben1369 13y ago
    I would agree. But there's nothing in here that's cause for concern legally. And PR folks are going to have a tough time overruling Elon based on "style" points. As I mentioned he probably sees nothing wrong with his approach and thus any PR comments would fall on deaf ears.
- OrwellianChild 13y ago
  It's unfortunate that our current media climate requires it, but a straightforward, "accept the inherent risks" approach to the problem would be massacred by news outlets. Were Musk to say something like this, headlines could read "Tesla's Billionaire Owner Disregards Model S Fire Hazzard" and not suffer libel. Particularly for people such as Musk, who are doing so much to advance the expectations of consumers and raise the bar for what is possible with new technology (and here I'm speaking as an un-abashed Musk supporter), I can't help but support his rigorous defense of his projects. Whether it's the NYT "review" that attempted to slam the Model S mile range or the astonishingly good crash ratings for the same car, I think it serves us all to let Musk use his soapbox to be an advocate for his work at Tesla, SpaceX, etc.
slipperyp 13y ago
I dislike that statement, too, but for different reasons. The 30,000x larger sample in the aggregate means the calculated fire rate for non-Tesla cars is probably a more reliable number. Maybe those 100M Tesla miles were "lucky"? Possibly not, though - I don't know enough about cars to guess. The 3 trillion aggregate miles includes a lot broader sample size of car age than those from a single company that's 10 years old. This, to me, seems important to control for. Finally - I bet the usage profile of a Tesla is different from the median usage profile of every random car on the street and throughout the country.
superfx 13y ago
I believe your reasoning is incorrect. If we model the number of fires by a poisson distribution (very reasonable), a single sample would correspond to the mode of the distribution. What you would like is an estimate of the mean, i.e. lambda. It so happens that the mode of a poisson distribution is floor(lambda) or ceiling(lambda)-1, and thus it is an underestimate of the mean. In other words, fires are likely to be less frequent than what a single sample suggests.
mark-r 13y ago
Apples to apples: how many car fires are started because the car is old and not in good repair? I'll bet the rate is much lower for gasoline cars less than a year old. We'll just have to wait to see how 10-year-old Teslas hold up.
bjornsing 13y ago
I'm a big fan of Elon but I think he may be way off with these numbers... :S If you read the reports from the National Fire Protection Association they do estimate the number of "highway vehicle fires" at around 150 000 per year [1], but they also explicitly say that 'the term “highway vehicle fires” is used to describe the type of vehicle, not the location of the fire' [2]. If you look at fires caused by collision or overturn (which I guess this would be classified as) that's only 4% of the total, or 6000 per year. 1. https://www.nfpa.org/safety-information/for-consumers/vehicles https://www.nfpa.org/safety-information/for-consumers/vehicl... 2. https://www.nfpa.org/research/statistical-reports/vehicles/vehicle-fire-trends-and-patterns https://www.nfpa.org/research/statistical-reports/vehicles/v...
- codex 13y ago
  According to some quick math, then, Teslas are 9x more likely to catch on fire from a collision than the average US car (1 / 5K) / (6K / 254M). I put the Tesla fire rate at one in 5000 per year because the average Tesla has been on the road for around half a year, and there are 10,000 of them.
- cwp 13y ago
  I bet you could get the number lower if you only counted fires caused by collision or overturn of a highway vehicle less than 3 years old. Or heck, just the black ones. Yes, this fire was caused by a collision, but fires caused by other things are relevant. If a Tesla car caught fire in somebody's driveway, people would be concerned about that too, right? So comparing 150,000 highway vehicle fires to 1 Tesla fire, regardless of cause, is pretty reasonable.
  - codex 13y ago
    In considering whether to buy a Tesla, I would evaluate the safety of the alternatives. Most in the market for a Tesla aren't going to buy the 23 year old Buick LeSabre whose oil leaks caught fire on the Jersey turnpike last week. So I think it's reasonable to compare the safety with a modern luxury sedan. I don't think as many of those catch fire without a collision.
m3mnoch 13y ago
if 100 million miles isn't enough to gain statistical significance, what number is?
scythe 13y ago
I think it's lamentable that we're all looking at the bulk, "brute-force" statistical reasoning instead of considering the details of the case and what that means for the fire safety of the car. The line you quoted was incidental, rather than necessary, to the substance of Musk's argument. Whether it's PR or not is ignoratio elenchi. If the battery really was punctured by an unfortunately placed piece of metal in a sort of surprising scenario, we ought to stratify by collision type in order to really understand the problem. How do gas cars perform during a gas tank puncture? At similar speeds? And how common are such collisions? The relevance of this consideration is expressed by Simpson's paradox: http://en.wikipedia.org/wiki/Simpson's_paradox http://en.wikipedia.org/wiki/Simpson's_paradox I.e. analyses of performance when conditions differ ought to take into account those conditions, at least when they are both a: known (true in this case) and b: not causally connected to the variable under consideration (also true in this case).
6ren 13y ago
Mr Market overreacts to bad news, and when a value investor buys. Agreed, there's insufficient data for meaningful statistics, but his main points were amour-plating, firewalls and that batteries are less fire-prone than "highly flammable liquid".
BHSPitMonkey 13y ago
Also, how many Tesla drivers are driving around in 10-year-old cars? There are plenty of avenues to explore in debunking that statistical hand-waving.

squidi 13y ago

> Americans drive an aggregate of 3 trillion miles, while Tesla drivers have done 100 million. That's well over an order of magnitude difference. The data on 100 million is probably enough to compare with the 3 trillion miles. The populations don't need to be equal to compare them, just big enough that they are random and distributed enough.

nonchalance 13y ago
To put it in perspective, the disparity is equivalent to polling 10K americans and extrapolating to all of america (which, for better or for worse, is what most pollsters do).
- ProCynic 13y ago
  If the sample is truly random, it doesn't matter what the population size is. Of course, truly random samples are hard to get.
  - adw 13y ago
    That depends on the population variance.
  - deleted 13y ago
    [deleted]
- akavi 13y ago
  Except pollsters put in a lot of effort in making sure that the sample is representative of the larger population. Which is not true here, as the GP correctly notes.
  - mikeash 13y ago
    Do they really? My only interaction with pollsters has been either having them call me or solicit me on the street, and both approaches have a tremendous inherent bias. As far as I know, this is how the big national agencies do things.
    - PeterisP 13y ago
      There are all kinds of adjustments done afterwards to correct for various factors. For example, you know the age distributions in USA; and if you find out your phone calls are getting twice as many seniors than the proportion should be[1], then you throw away a random parts of them so that they don't skew final 'data' towards the typical opinions of seniors. [1] Assuming that you're not measuring average age or measuring 'who is at home', but if you want to see, say, the average political opinion of total USA population, which tends to correlate with age.
      - mikeash 13y ago
        It still seems impossible to correct for everything. Sure, you could correct for age as you describe, but I imagine that landline phone ownership correlates with political opinions in all sorts of other ways too. Furthermore, how do you gather the data needed to correct the polling numbers without being able to accurately poll people in the first place? Seems like a complete chicken-and-egg problem.
        PeterisP 13y ago
        "how do you gather the data needed to correct the polling numbers" -> you use the census. You need some info about the total population, you get it periodically and it doesn't change that much; you don't need to repeat it for every survey.
- Zikes 13y ago
  I often see polls of 1K Americans and extrapolating out from there. An example: http://www.webpronews.com/americans-think-cloud-computing-comes-from-actual-clouds-2012-08 http://www.webpronews.com/americans-think-cloud-computing-co... Of course, the refrain I often hear is that as long as you pick the RIGHT 1,000 Americans, it's as good as polling all 319 million.
  - gnaritas 13y ago
    > Of course, the refrain I often hear is that as long as you pick the RIGHT 1,000 Americans, it's as good as polling all 319 million. If it's a proper random sample, then it's far better than sampling all 319 million because it's 95% accurate with about a 3% margin of error and vastly cheaper and actually practical; you can't poll 319 million people.
- mikeash 13y ago
  It's counterintuitive, but the sample size needed for a good measurement doesn't much depend on the size of the overall population. What matters is getting a properly random sample. This is where pollsters fall down, because their "random" sample tends to be heavily biased toward the sort of person who has a landline telephone and doesn't hang up on pollsters. Polling 10,000 Americans would be vast overkill, in any case.
- deleted 13y ago
  [deleted]
- gnaritas 13y ago
  You say that as if 10k is too small a sample size to extrapolate accurately with, but actually that's a huge sample size that if done properly would be extremely accurate. You don't need to poll anywhere near 10k people to accurately predict all Americans views. You can sample less than 2000 people and get 99% accuracy with a 3% margin of error for a population of 325 million. Increasing the sample size to 10k simply reduces the margin of error to 1.29%, hardly worth the extra sampling of 8k people.
- auctiontheory 13y ago
  If you haven't read Asimov's Election Day, I highly recommend it.
broostoryco 13y ago
We are comparing tail events with low probabilities.
gkoberger 13y ago
When trying to get popular opinion for, say, an election -- sure. However, there was one fire over 100 million miles. The problem isn't the 100 million, it's the 1 fire. This wasn't a controlled experiment, either -- they just stopped the clock as soon as the first fire happened, and multiplied. A week ago, they could have said "You have exactly a 0% chance of your Tesla catching on fire" and have been right by this logic. To think of it another way -- let's say you get lucky and get a hole-in-one your 10th time golfing. Does that mean you'll have 10 hole-in-ones if you golf 100 times? Doubtful. EDIT: Also, don't forget that Elon is mixing numbers. There's no fire if someone doesn't run over something. All these numbers show is that the average driver is more likely to run over something. Of course Tesla drivers run over fewer things -- there are no 16 year old kids texting while driving a Tesla... yet.
- revelation 13y ago
  Doesn't stopping the clock after 1 fire just penalize them, not benefit them? That said, I also think the 1 fire is the problem here. Just think about how that relation changes with 2 fires.
  - jamesaguilar 13y ago
    It probably penalizes them, assuming the no-fires-for-100m-miles was not a fluke. There's no way to know for sure without knowing the true distribution of fires per mile.
  - BWStearns 13y ago
    The chance goes from 0.000000010 to 0.000000020 If I had the cash I would still purchase a Tesla after the second fire as well.
    - sgustard 13y ago
      Thanks for converting that to "fires per mile".
    - moocowduckquack 13y ago
thedufer 13y ago
The relevant metric here seems to be 'miles between fire events'. On this metric, we have exactly 1 data point for Tesla. I would hardly call that "probably enough". Of course, I'm exaggerating in the other direction. What we really should be calculating is the odds that Teslas burst into flames less often than the average car, given that the average car does so every 20 million miles and the first such event in a Tesla was at the 100 million-mile mark. We're still failing to account for the fact that the average Tesla is newer and probably better-kept than the average car, but it would at least be a reasonable start. I don't know enough statistics to perform this calculation, but I would like to see how it is done.
- jurjenh 13y ago
  An easy starting point would be to get this kind of data on similarly aged cars - cars sold over the last 2-3 years, then see what stats you can get there. I'd guess that you'd find some models that have never caught fire and some that have done so a lot more than tesla's, but that's pure speculation on my part.
- PeterisP 13y ago
  We have enough events, because in this case it is appropriate to model the actual random event as 'million miles driven' with a chance of fire happening or not happening. Gasoline cars have a mean of 0.05 fires per million miles, and given the current Tesla data, the mean is 0.01 fires per million miles. I'm not taking out a calculator, but it would come out to an extremely low (0.0001%) the 'true' fire chance is the 0.05 gas car rate or higher; the 95% confidence interval should be 0.01 +- 0.02 or tighter, so still twice better than gas cars. For an exaggerated example, if Tesla had driven a billion miles and had 0 fires, you shouldn't say that there's not enough data - you definitely would have enough data to say that the chance of fire is below the gas-car rate of 5 fires per 100 million miles.
  - thedufer 13y ago
    Why is million miles driven a better way to model it than billion miles driven, for example? If you happen to choose that, there clearly isn't anywhere near enough data. I'm honestly curious how one models this type of thing statistically, and I am not convinced enough of its obviousness to just accept numbers that someone throws around.

grinich 13y ago

Hard to argue against Elon's last sentence, though.

deletes 13y ago
That should be the main point of his argument, instead of speculative statistics.

ececconi 13y ago

I agree, the exclamation mark was a terrible thing to include. Imagine if someone died, would they still put the exclamation mark there?

sologoub 13y ago

The page is as much about marketing (maybe more) as it is about safety or the incident. Especially, after the stock dropped, can you blame them? That said, I'm not really sure why this is such big news. Accident happened due to debris on the road. No one was hurt. The car was severely damaged, but got the owner to safety. AND THEN a small fire happened... Then I read things like this: http://www.dailynews.com/general-news/20130928/5-killed-1-injured-in-fiery-single-vehicle-crash-in-burbank http://www.dailynews.com/general-news/20130928/5-killed-1-in... Let's consider this for a second - Tesla Model S had a no-injury accident and made national news. 5 kids burned alive in a Sentra, and this barely stayed on local news for 3 days. Tesla Model S is a phenomenal vehicle with an excellent, if short-ish, track record. It really annoys me that reporters go out of their way for sensationalist articles, when there are far worse tragedies to cover.

baddox 13y ago
> The page is as much about marketing (maybe more) as it is about safety or the incident. What does that mean? Taking a common definition of "marketing" to be "expressing the value of a product to potential customers," any article that is about safety or about a recent product incident is also marketing. It sounds like you're using "marketing" as an ill-defined term that basically just means "something bad about the way a company publishes information."
- sologoub 13y ago
  "Bad" is subjective, when I personally think Marketing, I mean putting a spin on things and presenting it in a more favorable light for the company. This is not a dry facts page, but a public relations communication that is intended to sell you on the fact that Tesla Model S is a safe vehicle. Nothing wrong with that and nothing "bad" as you seemed to imply.
  - baddox 13y ago
    But all of the claimed facts are either true or false, right?

danso 13y ago

I agree...The kind of driver who can buy a Tesla is likely the kind of driver who has acquired enough education and comfortable wealth to be a competent driver (on the average). Moreover, there's survivor bias here: If you've made it far enough in life to buy a Tesla, you're probably a person with pretty decent habits. And finally, if you've bought an expensive car like the Tesla, you may be more likely to drive it more carefully than the average person does their Honda Accord. I don't think Musk is any more dishonest than any other CEO, and he's probably more honest, by far, on average. However, it kind of pains me to see how easy it is for him to sway the hacker crowd with data-interpretations that would be questionable by any standard. If this is among the strongest empirical evidence he can provide, then I think we should maintain some skepticism.

alxp 13y ago
A study by UC Berkeley and the University of Toronto actually showed that luxury car owners were by far the most aggressive drivers, and the least likely to stop for other road users. http://www.bankrate.com/financing/cars/study-bmw-drivers-are-the-worst/ http://www.bankrate.com/financing/cars/study-bmw-drivers-are... For whatever reason BMW stood out most of all as the worst of the worst in this study, but 'expensive car drivers are better drivers' has been proven to not be an assertion you can make from common sense or intuition.
- danso 13y ago
  Without reading the study, I'm ready to agree that its conclusions are correct. But I'd argue we're still comparing apples to oranges here: 1. We can't assume that Tesla drivers are the same as traditional luxury car drivers. While cars are a statement of wealth, and many arrogant bastards like making that statement...A Tesla is ostensibly a statement of a few other things, such as concern for the environment, optimism about technology, etc. etc...in the same way, even though many programmers make high-end salaries (low-6 figures), I wouldn't say that we can expect these programmers to golf as much as the average non-programmer low-6-figure-earner. 2. Reading the link you posted, it said the study evaluated based on the frequency of accidents and the size of payout...I couldn't find the study on the website, but this statement from the article was ambiguous to me: > According to data from IIHS website, the collision insurance losses on BMW 7 Series are more than twice the average for vehicles nationwide, and BMW 3 Series two-doors are more than three times. Twice the average of what...? Payouts total? Payouts per claim? Payouts per claim normalized by number of total cars of that kind on the road? 3. The NHTS data concerns the number of fires. For the study you cited to be more relevant, we'd have to know what proportion of the insurance claims also involve vehicle fires. If you're thinking, "Well, if a car caught on fire, then that's likely because of an accident...so more accidents mean more fires"...well, a> That's a classic logical fallacy (All dogs are animals. Sara owns a lot of animals. Therefore, Sara owns a lot of dogs) and b> the kinds of accidents that make up a majority of insurance claims (my guess is low-to-medium speed fender benders) may not represent a significant portion of incidents that end up in a flaming wreck. All in all, I wouldn't say that Musk is clearly wrong here...He could be right, we just don't have enough information either way...so it feels slightly dirty -- a slap in the face of analytical thinking -- for him to cite these statistics as being anywhere near conclusive.

sz4kerto 13y ago

> I agree this isn't as big of a deal as the stockmarket may imply I firmly believe that what's happening on the stockmarket and the fire are merely a coincidence, there isn't a causal relation between them. Tesla stock has been due to correct back for a while, and a downgrade came in as well (unrelated to the fire). Edit: first rule of the HN club: only positive things about Tesla, otherwise you are going to be voted down. Neutral opinion is considered negative. :)

eridius 13y ago

> Plus, the average Tesla driver is currently probably a superior driver I can play the conjecture game too. The average Tesla driver is probably a worse driver than the average gas-powered car driver. Why? Because they have the disposable income to purchase a Tesla, which means they're probably less careful with their possessions (as they can presumably afford to replace them), plus the Model S is a sports car so they're probably driving faster and more carefree than your average person. Not that I really believe this, but come on, your argument is completely made up.

SEJeff 13y ago
I would counter with, "How dare you assume that all Tesla drivers have disposable income to throw around". I happen to be close to buying one and know a few other owners who are average middleish class people who normally would have bought a porsche or a tesla. I work in tech and as a result am paid pretty decent. Do I have disposable money (or my friends) to buy a Tesla Model S? No! However, given where I live and where I want to drive + the recharging stations, Tesla is a good option for me. Do not assume just because someone is able to get enough money to buy something expensive,that they have tons of money. By that same logic, anyone who is able to buy a home is clearly flush with cash and able to throw it all around. Completely ridiculous.
- dandelany 13y ago
  You're missing the point - he's not actually making that argument, he's showing how easy it is to make any argument if you back it up with anecdotal conjecture rather than data.
  - eridius 13y ago
    Exactly. I rather suspect that Tesla drivers are actually comparable to other drivers, rather than being demonstrably better or worse, but the only way to know would be to actually conduct a study on the subject.
    - 13y ago

larrys 13y ago

"they have a brand new expensive car" A good point. It would be interesting to compare the miles drive on "brand new expensive cars" not just all cars which include obviously older and/or poorly maintained vehicles.

baddox 13y ago
Why would that be relevant? Anyone who buys a Tesla Model S will instantly be in the category of "people who buy brand new expensive cars," so the Model S stats are sufficient.
- kschults 13y ago
  That's the point. larrys wants to compare the Model S miles driven by "people who buy brand new expensive cars" against other car miles driven by "people who buy brand new expensive cars," instead of comparing the Model S miles [...] against other car miles driven by everyone.

codex 13y ago

This comparison is a bit off. Most of the cars which catch fire are old. The comparison should be to a similarly priced, brand new luxury car. Very few of those catch fire, either.

bborud 13y ago
Well, then I would limit it to Ferraris that are 3 years or younger :).

jusben1369 13y ago

I think this is Elon's one blind spot. For a engineer he's awfully "salesy" at times. The whole lease thing was really distasteful. This less so; but still a bit awkward. Why not just end with "Fires are unfortunately a risk for electric and gasoline cars. Each year in the US there are more than 150,000 fires. As more and more Tesla's enter the world we're going to experience all manner of events" That would be the right way to put this in context. However, I suspect that to overcome the naysayers and truly change a market (electric cars) requires an almost insane love for what you do - which makes you sound a little too defensive when something goes wrong.

_delirium 13y ago
I have no idea how Tesla operates internally, but I wouldn't be too surprised if, like at most companies, letters that go out under the CEO's name are vetted by both the legal and PR departments, and possibly written or edited by them. If that's the case, then "Elon Musk" is a sort of composite entity, which includes a human named "Elon Musk", but not solely that human.
- jusben1369 13y ago
  I would agree. But there's nothing in here that's cause for concern legally. And PR folks are going to have a tough time overruling Elon based on "style" points. As I mentioned he probably sees nothing wrong with his approach and thus any PR comments would fall on deaf ears.
OrwellianChild 13y ago
It's unfortunate that our current media climate requires it, but a straightforward, "accept the inherent risks" approach to the problem would be massacred by news outlets. Were Musk to say something like this, headlines could read "Tesla's Billionaire Owner Disregards Model S Fire Hazzard" and not suffer libel. Particularly for people such as Musk, who are doing so much to advance the expectations of consumers and raise the bar for what is possible with new technology (and here I'm speaking as an un-abashed Musk supporter), I can't help but support his rigorous defense of his projects. Whether it's the NYT "review" that attempted to slam the Model S mile range or the astonishingly good crash ratings for the same car, I think it serves us all to let Musk use his soapbox to be an advocate for his work at Tesla, SpaceX, etc.

slipperyp 13y ago

I dislike that statement, too, but for different reasons. The 30,000x larger sample in the aggregate means the calculated fire rate for non-Tesla cars is probably a more reliable number. Maybe those 100M Tesla miles were "lucky"? Possibly not, though - I don't know enough about cars to guess. The 3 trillion aggregate miles includes a lot broader sample size of car age than those from a single company that's 10 years old. This, to me, seems important to control for. Finally - I bet the usage profile of a Tesla is different from the median usage profile of every random car on the street and throughout the country.

superfx 13y ago

I believe your reasoning is incorrect. If we model the number of fires by a poisson distribution (very reasonable), a single sample would correspond to the mode of the distribution. What you would like is an estimate of the mean, i.e. lambda. It so happens that the mode of a poisson distribution is floor(lambda) or ceiling(lambda)-1, and thus it is an underestimate of the mean. In other words, fires are likely to be less frequent than what a single sample suggests.

mark-r 13y ago

Apples to apples: how many car fires are started because the car is old and not in good repair? I'll bet the rate is much lower for gasoline cars less than a year old. We'll just have to wait to see how 10-year-old Teslas hold up.

bjornsing 13y ago

I'm a big fan of Elon but I think he may be way off with these numbers... :S If you read the reports from the National Fire Protection Association they do estimate the number of "highway vehicle fires" at around 150 000 per year [1], but they also explicitly say that 'the term “highway vehicle fires” is used to describe the type of vehicle, not the location of the fire' [2]. If you look at fires caused by collision or overturn (which I guess this would be classified as) that's only 4% of the total, or 6000 per year. 1. https://www.nfpa.org/safety-information/for-consumers/vehicles https://www.nfpa.org/safety-information/for-consumers/vehicl... 2. https://www.nfpa.org/research/statistical-reports/vehicles/vehicle-fire-trends-and-patterns https://www.nfpa.org/research/statistical-reports/vehicles/v...

codex 13y ago
According to some quick math, then, Teslas are 9x more likely to catch on fire from a collision than the average US car (1 / 5K) / (6K / 254M). I put the Tesla fire rate at one in 5000 per year because the average Tesla has been on the road for around half a year, and there are 10,000 of them.
cwp 13y ago
I bet you could get the number lower if you only counted fires caused by collision or overturn of a highway vehicle less than 3 years old. Or heck, just the black ones. Yes, this fire was caused by a collision, but fires caused by other things are relevant. If a Tesla car caught fire in somebody's driveway, people would be concerned about that too, right? So comparing 150,000 highway vehicle fires to 1 Tesla fire, regardless of cause, is pretty reasonable.
- codex 13y ago
  In considering whether to buy a Tesla, I would evaluate the safety of the alternatives. Most in the market for a Tesla aren't going to buy the 23 year old Buick LeSabre whose oil leaks caught fire on the Jersey turnpike last week. So I think it's reasonable to compare the safety with a modern luxury sedan. I don't think as many of those catch fire without a collision.

m3mnoch 13y ago

if 100 million miles isn't enough to gain statistical significance, what number is?

scythe 13y ago

I think it's lamentable that we're all looking at the bulk, "brute-force" statistical reasoning instead of considering the details of the case and what that means for the fire safety of the car. The line you quoted was incidental, rather than necessary, to the substance of Musk's argument. Whether it's PR or not is ignoratio elenchi. If the battery really was punctured by an unfortunately placed piece of metal in a sort of surprising scenario, we ought to stratify by collision type in order to really understand the problem. How do gas cars perform during a gas tank puncture? At similar speeds? And how common are such collisions? The relevance of this consideration is expressed by Simpson's paradox: http://en.wikipedia.org/wiki/Simpson's_paradox http://en.wikipedia.org/wiki/Simpson's_paradox I.e. analyses of performance when conditions differ ought to take into account those conditions, at least when they are both a: known (true in this case) and b: not causally connected to the variable under consideration (also true in this case).

6ren 13y ago

Mr Market overreacts to bad news, and when a value investor buys. Agreed, there's insufficient data for meaningful statistics, but his main points were amour-plating, firewalls and that batteries are less fire-prone than "highly flammable liquid".

BHSPitMonkey 13y ago

Also, how many Tesla drivers are driving around in 10-year-old cars? There are plenty of avenues to explore in debunking that statistical hand-waving.