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It saddens me and depresses me greatly regarding the job prospects of working with statistics in modern tech companies when I read articles like this. I know o
by p4wnc6 11y ago
It saddens me and depresses me greatly regarding the job prospects of working with statistics in modern tech companies when I read articles like this.
I know others will disagree with me, but my feeling after working in a number of jobs in which large systems were built to automate large-scale frequentist hypothesis testing operations is that these methods just wholly fail, and that business politics leads people to read whatever conclusions they'd like to from the results, and give credit back to the statistical framework even if it is not deserved.
I should be careful not to over-state this too much. I understand there is a mathematical framework for these tools and despite being trained in machine learning and Bayesian methods, almost all of my professional experience has been working with frequentist statistics. Sometimes you have enough data that it would probably swamp out whatever prior you might choose; often you don't have (or want to invest in getting) expert priors, and "non-informative priors" and that ilk sort of rope in some of the same problems as what frequentism has. You can get a limited amount of evidence from doing simple frequentist things, but you also open the door for all of the misunderstandings of p-values, ignoring effect sizes, doing model selection by directly comparing t-stats, etc., which just seems to be way, way less of a problem if you use other methods.
Some of the main sources of enlightenment for me on this have been:
[0] http://lesswrong.com/lw/g13/against_nhst/ http://lesswrong.com/lw/g13/against_nhst/
[1] http://www.columbia.edu/~gjw10/achen04.pdf http://www.columbia.edu/~gjw10/achen04.pdf
[2] http://www.indiana.edu/~kruschke/articles/Kruschke2012JEPG.pdf http://www.indiana.edu/~kruschke/articles/Kruschke2012JEPG.p...
The last article, by Kruschke, spends a lot of time on exactly the type of issue from the Twitter article -- something like two-group mean testing.
In general, I cannot understand why people continue to use frequentist methods on policy problems -- that is, problems where you are inherently looking for Pr(Hypothesis | Data), and where, due to all of the many, many pitfalls from the above sources and elsewhere, you can be sure that Pr(Data | Hypothesis) is not at all a suitable proxy for Pr(Hypothesis | Data).
I would view any labor costs associated with figuring out why A/A/B testing is not a useful idea to be pure waste, not because the math is wrong or anything (the math is interesting and good!) but because, from first principles, this just seems like totally and completely the wrong way to approach this kind of applied problem.
And yet, everyone is doing it, and baking it right into their huge production analytics systems -- most notoriously all of the modern fly-by-night marketing tech startups.
- squarecog 11y agoCo-author of the Twitter post here. I don't necessarily disagree with you! Though I hope you are not calling Twitter a fly-by-night marketing startup :). As a company, we've found A/B testing very valuable, but it certainly has limitations, and pitfalls that one must be fairly experienced to avoid. You can see some descriptions of what we do to achieve that in other posts in that series. But it's fair to say that this takes some work (like the work described in the "second control" post) to avoid badness, and it's fair to question if other methods can get us to the same end result -- ability to evaluate impact of proposed product changes -- cheaper, or more accurately.
- p4wnc6 11y ago> Though I hope you are not calling Twitter a fly-by-night marketing startup :) That remains to be seen.
- mabbo 11y agoSo how would you test things differently? I'm not being facetious here: you sound like you have a good grasp of statistics, and I only have a minor in math (and a love of good number crunching). At the end of the day, we need to be able to tell management that we believe the change had this big of an effect, within these errors bars. Management need that in order to make financial decisions. They aren't dumb, but they also can't be expected to have a masters in statistics.
- p4wnc6 11y agoA perfectly reasonable alternative, which is not really any more mathematically difficult nor harder to implement in software, is outlined in several sections of the Kruschke paper that I linked. In general though, I would dispute a lot of your claims about what industry statisticians (or "data scientists" if you want to use a buzzword) need to do. One of the primary jobs of industry statisticians, it would seem, should be to slow everyone down on purpose, because everyone is in such a rush to get "insight" and "actionable information" and to get some sweet data viz of some KPIs that they are doing horribly shoddy statistics, and mutating the craft of statistics overall into some kind of shoddy data journalism / data story telling circus where the careful avoidance of statistical pitfalls doesn't seem to matter to anyone.