An Example of p-Hacking

Vincent Granville explains why using p-values for model-worthiness can lead you to a bad outcome:

Recently, p-values have been criticized and even banned by some journals, because they are used by researchers, who cherry-pick observations and repeat experiments until they obtain a p-value worth publishing to obtain grant money, get tenure, or for political reasons.  Even the American Statistical Association wrote a long article about why to avoid p-values, and what you should do instead: see here.  For data scientists, obvious alternatives include re-sampling techniques: see here and here. One advantage is that they are model-independent, data-driven, and easy to understand. 

Here we explain how the manipulation and treachery works, using a simple simulated data set consisting of purely random, non-correlated observations. Using p-values, you can tell anything you want about the data, even the fact that the features are highly correlated, when they are not. The data set consists of 16 variables and 30 observations, generated using the RAND function in Excel. You can download the spreadsheet here.

And for a more academic treatment of the problem, I love this paper by Andrew Gelman and Eric Loken, particularly because it points out that you don’t have to have malicious intent to end up doing the wrong thing.

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