Predictive relationships and A/B testing

I recently watched an interesting webinar on Seeking the Magic Optimization Metric: When Complex Relationships Between Predictors Lead You Astray by Kelly Uphoff, manager of experimental analytics at Netflix. The presenter mentioned that Netflix is a heavy user of A/B testing for experimentation, and in this talk focused on the goal of optimizing retention. In ideal A/B testing, the company would test the effect of an intervention of choice (such as displaying a promotion on their website) on retention, by assigning it to a random sample of users, and then comparing retention of the intervention group to that of a control … Continue reading Predictive relationships and A/B testing

No correlation -> no causation?

I found an interesting variation on the “correlation does not imply causation” mantra in the book Applied Multiple Regression/Correlation Analysis for the Behavioral Sciences by Cohen et al. (apparently one of the statistics bibles in behavioral sciences). The quote (p.7) looks like this: Correlation does not prove causation; however, the absence of correlation implies the absence of the existence of a causal relationship Let’s let the first part rest in peace. At first glance, the second part seems logical: you find no correlation, then how can there be causation? However, after further pondering I reached the conclusion that this logic is flawed, … Continue reading No correlation -> no causation?

Beer and … crime

I often glimpse the local newspapers while visiting a foreign country (as long as it is in a language I can read). Yesterday, the Australian Herald Sun had the article “Drop in light beer sales blamed for surge in street violence“. The facts presented: “Light beer sales have fallen 15% in seven years, while street crime has soared 43%”. More specifically: “Police statistics show street assaults rose from 6400 in 2000-01 to more than 9000 in 2007-08. At the same time, Victorians’ thirst for light beer dried up.” The interpretation by health officials: “there was a definite connection between the … Continue reading Beer and … crime