Bert Gunter points to this New York Times article, “How Exercise May Make Us Healthier: People who exercise have different proteins moving through their bloodstreams than those who are generally sedentary,” writing that it is “hyping a Journal of Applied Physiology paper that is now my personal record holder for most extensive conclusions from practically no data by using all possible statistical (appearing) methodology . . . I [Gunter] find it breathtaking that it got through peer review.”
OK, to dispose of that last issue first, I’ve seen enough crap published by PNAS and Lancet to never find it breathtaking that anything gets through peer review.
But let’s look at the research paper itself, “Habitual aerobic exercise and circulating proteomic patterns in healthy adults: relation to indicators of healthspan,” by Jessica Santos-Parker, Keli Santos-Parker, Matthew McQueen, Christopher Martens, and Douglas Seals, which reports:
In this exploratory study, we assessed the plasma proteome (SOMAscan proteomic assay; 1,129 proteins) of healthy sedentary or aerobic exercise-trained young women and young and older men (n = 47). Using weighted correlation network analysis to identify clusters of highly co-expressed proteins, we characterized 10 distinct plasma proteomic modules (patterns).
Here’s what they found:
In healthy young men and women, 4 modules were associated with aerobic exercise status and 1 with participant sex. In healthy young and older men, 5 modules differed with age, but 2 of these were partially preserved at young adult levels in older men who exercised; among all men, 4 modules were associated with exercise status, including 3 of the 4 identified in young adults.
Uh oh. This does sound like a mess.
On the plus side, the study is described right in the abstract as “exploratory.” On the minus side, the word “exploratory” is not in the title, nor did it make it into the news article. The journal article concludes as follows:
Overall, these findings provide initial insight into circulating proteomic patterns modulated by habitual aerobic exercise in healthy young and older adults, the biological processes involved, and the relation between proteomic patterns and clinical and physiological indicators of human healthspan.
I do think this is a bit too strong. The “initial” in “initial insight” corresponds to the study being exploratory, but it does not seem like enough of a caveat to me, especially considering that the preceding sentences (“We were able to characterize . . . Habitual exercise-associated proteomic patterns were related to biological pathways . . . Several of the exercise-related proteomic patterns were associated . . .”) had no qualifications and were written exactly how you’d write them if the results came from a preregistered study of 10,000 randomly sampled people rather than an uncontrolled study of 47 people who happened to answer an ad.
How to analyze the data better?
But enough about the reporting. Let’s talk about how this exploratory study should’ve been analyzed. Or, for that matter, how it can be analyzed, as the data are still there, right?
To start with, don’t throw away data. For example, “Outliers were identified as protein values ≥ 3 standard deviations from the mean and were removed.” Huh?
Also this: “Because of the exploratory nature of this study, significance for all subsequent analyses was set at an uncorrected α < 0.05." This makes no sense. Look at everything. Don't use an arbitrary threshold. Also there's some weird thing in which proteins were divided into 5 categories. It's kind of a mess. To be honest, I'm not quite sure what should be done here. They're looking at 1129 different proteins so some sort of structuring needs to be done. But I don't think it makes sense to do the structuring based on this little dataset from 47 people. A lot must already be known about these proteins, right? So I think the right way to go would be to use some pre-existing structuring of the proteins, then present the correlations of interest in a grid, then maybe fit some sort of multilevel model. I fear that the analysis in the published paper is not so useful because it's picking out a few random comparisons, and I'd guess that a replication study using the same methods would come up with results that are completely different. Finally, I hove no doubt that the subtitle of the news article, "People who exercise have different proteins moving through their bloodstreams than those who are generally sedentary," is true, because any two groups of people will differ in all sorts of ways. I think the analysis as performed won't help much in understanding these differences in the general population, but perhaps a multilevel model, along with more data, could give some insight. P.S. Maybe the title of this post could be compressed to the following: Random in, random out.