Suggestions for future articles are welcomed as comments to this entry. Some topics I intend to write about are listed below.

- Matching vs. covariate adjustment (see below from Arne Warnke)
- Statistical strategy for propensity score modeling and usage
- What is the full meaning of a posterior probability?
- Moving from pdf to html for statistical reporting
- Is machine learning statistics or computer science?
- Sample size calculation: Is it voodoo?
- Difference between Bayesian modeling and frequentist inference

A few weeks ago we had a small discussion at CrossValidated about the pros and cons of matching here. I am sorry that I did not had enough time to elaborate further on the support of matching procedures (in my field researchers do not focus much on a bias-variance tradeoff but they prioritize on minimizing biases. For that reason, they like matching procedures). Now, I have seen that you started a blog recently (congratulations!). I would like to encourage to take up the topic of matching because it is probably interesting for many applied researchers. I think in your ‘philosophy’, this would belong to the point “Preserve all the information in the data”. Here, perhaps some input for a blog post. Back then, you wrote:

Matching on continuous variables results in an incomplete adjustment because the variables have to be binned.

What about propensity score matching?

Matching throws away good data from observations that would be good matches.

Extrapolation bias is only a significant problem if there is a covariate by group interaction, and users of matching methods ignore interactions anyway.

Here, you go too far (in my view). You can add interactions, again for example with propensity score matching. Imbens and Rubin (2015) suggest a procedure using quadratic and interaction terms of the covariates.

Comment: Nice to know this exists but I’ve never seen a paper that used matching attempt to explore interactions. If you don’t want to make regression assumptions that are unverifiable, remove observations outside the overlap region just as with matching.

Which assumptions do you refer to? I think that treating everyone the same (statistically) is also an unverifiable assumption (do you disagree?). What is your opinion about weighted least squares?

Comment: This is the no-interaction assumption. If you assume additivity then it’s more OK to have a no-overlap region, otherwise throw-away non-overlap regions and do a conditional analysis. Not clear on the need for weighting here. In general I like conditioning over weighting.

Arne Jonas Warnke

Labour Markets, Human Resources and Social Policy

Internet: zew.de