01 May 2019

The results of my crowdsourced reanalysis project

Just over a year ago, in this post, I asked for volunteers to help me reanalyze an article that I had read entirely by chance, and which seemed to have a few statistical issues. About ten people offered to help, and three of them (Jan van Rongen, Jakob van de Velde, and Matt Williams) stayed the course. Today we have released our preprint on PsyArXiv detailing what we found.

The article in question is "Is Obesity Associated with Major Depression? Results from the Third National Health and Nutrition Examination Survey" (2003) by Onyike, Crum, Lee, Lyketsos, and  Eaton. This has 951 citations according to Google Scholar, making it quite an important paper in the literature on obesity and mental health. As I mentioned in my earlier blog post, I contacted the lead author, Dr. Chiadi Onyike, when I first had questions about the paper, but our correspondence petered out before anything substantial was discussed.

It turns out that most of the original problems that I thought I had found were due to me misunderstanding the method; I had overlooked that the authors had a weighted survey design. However, even within this design, we found a number of issues with the reported results. The power calculations seem to be post hoc and may not have carried out appropriately; this makes us wonder whether the main conclusion of the article (i.e., that severe obesity is strongly associated with major depressive disorder) is well supported. There are a couple of simple transcription errors in the tables, which as a minimum seem to merit a correction. There are also inconsistencies in the sample sizes.

I should make it clear that there is absolutely no suggestion of any sort of misconduct here. Standards of reproducibility have advanced considerably since Onyike et al.'s article was published, as has our understanding of statistical power; and the remaining errors are of the type that anyone who has tried to assemble results from computer output into a manuscript will recognise.

I think that all four of us found the exercise interesting; I know I did. Everyone downloaded the publicly available dataset separately and performed their analyses independently, until we pooled the results starting in October of this year. We all did our analyses in R, whereas I had hoped for more diversity (especially if someone had used Stata, which is what the original authors used); however, this had the advantage that I was able to combine everybody's contribution into a single script file. You can find the summary of our analyses in an OSF repository (the URL for which is in the preprint).

We intend to submit the preprint for publication, initially to the American Journal of Epidemiology (where the original article first appeared). I'll post here if there are any interesting developments.

If you have something to say about the preprint, or any questions or remarks that you might have about this way of doing reanalyses, please feel free to comment!

1 comment:

  1. This is an interesting approach. I worked for the NHANES program for many years and have read many published articles from NHANES that have errors, including failing to use the sample weights and misunderstanding or misinterpretation of the data. By the way, Blank but applicable means that the individual was eligible to have the question asked but there is no response (as opposed to the situation where the skip pattern meant that the individual would not have been asked the question.) Misunderstanding of the skip pattern is also not uncommon. It should be remembered that the NHANES is a survey, and analyses such as the Onyike analysis (of which there are hundreds or perhaps thousands in the literature) are secondary analyses of data collected for a different purpose.