5 ms·

> sorry, saying 4/5 doctors recommend X is not a rational cue to buy X If we assume for a moment that 4/5 doctors really do recommend X, and that X is somethin

> sorry, saying 4/5 doctors recommend X is not a rational cue to buy X If we assume for a moment that 4/5 doctors really do recommend X, and that X is something related to one's health, why is it not a rational cue to buy X?

DanBC 12y ago
Doctors are human and are subject to the same cognitive biases as everyone else. What you want is a bunch of statisticians looking at the research and patient outcomes.
- philh 12y ago
  If 4/5 dentists (with no financial motivations) were asked "is there one brand of toothpaste in particular that you recommend?" and answered "toothident", then that would be a sensible reason to use toothident. (If a bunch of statisticians looked at the research and patient outcomes and disagreed, then that would be an even more sensible reason not to. But in lieu of that, we expect dentists to have a reasonable idea what they're talking about.) What actually happens (or so I hear) is that dentists are asked "do you recommend brushing twice a day with toothpastes such as toothident", and they say yes, because even though they've never heard of toothident, brushing your teeth is a good idea. So an ad that seys "4/5 dentists recommend toothident" doesn't actually mean that 4/5 dentists recommend toothident, and is not a sensible reason to buy toothident. But the way people interpret the ad is a sensible reason to buy toothident, it's just false.
  - DanBC 12y ago
    > If 4/5 dentists (with no financial motivations) were asked "is there one brand of toothpaste in particular that you recommend?" and answered "toothident", then that would be a sensible reason to use toothident. No! Just because they think it works doesn't mean it does work. Toothident might be the first toothpaste that comes to mind but that doesn't mean it's better than any other toothpaste - and it might be worse than other toothpastes. Perhaps the toothident company just have much better pens and sticky fixit pads than the other toothpaste companies.
    - philh 12y ago
      Yes, those things might be true. But I don't know anything about the pens and sticky fixit pads of the different toothpaste companies, and I have no reason to expect it correlates (in either direction) with toothpaste quality, so knowing this shouldn't change my decision. It should make me less confident in my decision, but not change it. Toothident is more likely to be recommended by 4/5 dentists in a world where it is better than other toothpastes, than in a world where it is worse. So by Bayes theorem, if we see that 4/5 dentists recommend toothident, this is evidence that toothident is better than other brands of toothpaste. It's not necessarily strong evidence, but it is definitely evidence. (And I do actually think it's fairly strong, if you can get 4/5 dentists to specifically recommend that one without priming them.)
      - lotsofmangos 12y ago
        Toothident is more likely to be recommended by 4/5 dentists if it is much better known than the best toothpaste, and advertising achieves that. Edit- Also dentists are not necessarily particularly rational. I know a dentist who told me that she rejects evidence based medicine and thinks that we should use traditional Chinese medicine instead. She isn't Chinese, she is a British middle-class hippy and when I asked her about the effect on rare species, she said that rare species are never used in Chinese medicine. I then asked her if she supports evidence based medicine when her patients are anesthetized, or does she think the dosage should be guessed and she said she didn't know what that had to do with it. Also, 5 is a tiny sample. From a sample of 5 dentists, 4 might tell you that the second coming of Christ is imminent, but that would tell you very little about either Christ's travel plans, or the opinions of dentists.
      - DanBC 12y ago
        > Toothident is more likely to be recommended by 4/5 dentists in a world where it is better than other toothpastes, than in a world where it is worse. This is false and it is dangerous. Dentists are not experts in toothpaste; they're not experts in the latest toothpaste research. A dentist recommending toothident will probably have no idea about whether toothident is better or worse than some other toothpaste. For a real world example of this see knee arthroscopy for rheumatoid arthritis. Doctors would recommend this surgery over other treatments until placebo[1] controlled trials found little benefit. "X out of Y experts recommend $THING" would be a terrible reason to chose $THING over $OTHERTHING unless you have imformation about why they recommend it and how they made that decision.
coldcode 12y ago
The ads never mention that they actual asked 100 dentists, found 4 who recommended it, added one of the non recommending ones to make it seem less cheesy, resulting in 4 out of 5 that we picked recommending our product. There is no law requiring a mention of the other 95 opinions.

DanBC 12y ago

Doctors are human and are subject to the same cognitive biases as everyone else. What you want is a bunch of statisticians looking at the research and patient outcomes.

philh 12y ago
If 4/5 dentists (with no financial motivations) were asked "is there one brand of toothpaste in particular that you recommend?" and answered "toothident", then that would be a sensible reason to use toothident. (If a bunch of statisticians looked at the research and patient outcomes and disagreed, then that would be an even more sensible reason not to. But in lieu of that, we expect dentists to have a reasonable idea what they're talking about.) What actually happens (or so I hear) is that dentists are asked "do you recommend brushing twice a day with toothpastes such as toothident", and they say yes, because even though they've never heard of toothident, brushing your teeth is a good idea. So an ad that seys "4/5 dentists recommend toothident" doesn't actually mean that 4/5 dentists recommend toothident, and is not a sensible reason to buy toothident. But the way people interpret the ad is a sensible reason to buy toothident, it's just false.
- DanBC 12y ago
  > If 4/5 dentists (with no financial motivations) were asked "is there one brand of toothpaste in particular that you recommend?" and answered "toothident", then that would be a sensible reason to use toothident. No! Just because they think it works doesn't mean it does work. Toothident might be the first toothpaste that comes to mind but that doesn't mean it's better than any other toothpaste - and it might be worse than other toothpastes. Perhaps the toothident company just have much better pens and sticky fixit pads than the other toothpaste companies.
  - philh 12y ago
    Yes, those things might be true. But I don't know anything about the pens and sticky fixit pads of the different toothpaste companies, and I have no reason to expect it correlates (in either direction) with toothpaste quality, so knowing this shouldn't change my decision. It should make me less confident in my decision, but not change it. Toothident is more likely to be recommended by 4/5 dentists in a world where it is better than other toothpastes, than in a world where it is worse. So by Bayes theorem, if we see that 4/5 dentists recommend toothident, this is evidence that toothident is better than other brands of toothpaste. It's not necessarily strong evidence, but it is definitely evidence. (And I do actually think it's fairly strong, if you can get 4/5 dentists to specifically recommend that one without priming them.)
    - lotsofmangos 12y ago
      Toothident is more likely to be recommended by 4/5 dentists if it is much better known than the best toothpaste, and advertising achieves that. Edit- Also dentists are not necessarily particularly rational. I know a dentist who told me that she rejects evidence based medicine and thinks that we should use traditional Chinese medicine instead. She isn't Chinese, she is a British middle-class hippy and when I asked her about the effect on rare species, she said that rare species are never used in Chinese medicine. I then asked her if she supports evidence based medicine when her patients are anesthetized, or does she think the dosage should be guessed and she said she didn't know what that had to do with it. Also, 5 is a tiny sample. From a sample of 5 dentists, 4 might tell you that the second coming of Christ is imminent, but that would tell you very little about either Christ's travel plans, or the opinions of dentists.
    - DanBC 12y ago
      > Toothident is more likely to be recommended by 4/5 dentists in a world where it is better than other toothpastes, than in a world where it is worse. This is false and it is dangerous. Dentists are not experts in toothpaste; they're not experts in the latest toothpaste research. A dentist recommending toothident will probably have no idea about whether toothident is better or worse than some other toothpaste. For a real world example of this see knee arthroscopy for rheumatoid arthritis. Doctors would recommend this surgery over other treatments until placebo[1] controlled trials found little benefit. "X out of Y experts recommend $THING" would be a terrible reason to chose $THING over $OTHERTHING unless you have imformation about why they recommend it and how they made that decision.

coldcode 12y ago

The ads never mention that they actual asked 100 dentists, found 4 who recommended it, added one of the non recommending ones to make it seem less cheesy, resulting in 4 out of 5 that we picked recommending our product. There is no law requiring a mention of the other 95 opinions.