Doing More With Null Age Effects: Introduction to the Special Section.

When I became editor of the Psychological Sciences section of the Journal of Gerontology, one of my first goals was to encourage awareness of equivalence tests for null effects to researchers studying psychological aging. A number of techniques were out there for evaluating the potential meaningfulness of null effects—termed “equivalence tests”—but aging researchers were by and large not using them. This was especially problematic for our field because we are in the business of investigating differences between (age) groups, and there is at least a lot of anecdotal evidence of studies that did not find significant (age) group differences also not being publishable in top aging journals. The typical reason for manuscripts with null age effects to be rejected is the inherent ambiguity of null results; however, equivalence tests can make them somewhat less ambiguous. If potentially meaningful null age effects are systematically missing from the literature, this would lead to overestimates of the magnitude of actual age differences in the published record. Publishing only papers with significant age differences may also encourage questionable research practices like p-hacking, as authors try to get to the all-important statistically significant age difference. It seems logically unlikely that every psychological process of interest varies with age (Isaacowitz, 2018). Thus, a robust and credible science of psychological studies of aging needs to be able to work with null age effects rather than doom them all to the file drawer (see also Isaacowitz & Lind, 2019). The article by Lakens, McLatchie, Isager, Scheel, and Dienes (this issue) that is the capstone of this special section is therefore a tutorial meant to walk aging researchers through examples of how they can make more of null age effects using equivalence testing. They provide both frequentist and Bayesian approaches to equivalence testing. The frequentist version is called two one-sided tests (TOST) and yields a p value that can be interpreted as in support of groups being similar (or not supporting that conclusion). The Bayesian version involves using Bayes factors to index support for one (vs. an alternative) hypothesis. In both cases, there are some guidelines for determining whether a null effect is supported as meaningful or remains ambiguous: the p value in TOST, and the magnitude of the Bayes factor in the Bayesian approach (and/or model comparisons with vs. without age included). Thus, an important caveat about equivalence testing is that it will not render meaningful just any and all null age effect findings. Instead, it provides a set of tests to evaluate which null age effects seem meaningful versus which ones continue to be ambiguous. One especially important feature of the article by Lakens and colleagues is that the example studies from the journal are not included to target their omission of the equivalence tests; the point is instead that these approaches may not have been available to the authors, but using the equivalence tests may lead to different and/or stronger conclusions, at least in some cases. Sometimes, equivalence tests will provide evidence for actual age similarity; other times, the equivalence tests will only tell us that we still do not know whether the age groups are similar or not. In these latter cases, we are left with the traditional ambiguity of null effects. So, equivalence tests help us distinguish between potentially meaningful and likely ambiguous null effects, but do not render all null effects meaningful. This point is reinforced by the important work presented in the article by Brydges and Bielak (this issue). In reviewing published studies in aging journals, they find that Bayes factors in particular have been used rarely so far—a point that is perhaps not too surprising. More importantly though, they do calculate Bayes factors for those studies Journals of Gerontology: Psychological Sciences cite as: J Gerontol B Psychol Sci Soc Sci, 2020, Vol. 75, No. 1, 42–44 doi:10.1093/geronb/gbz123 Advance Access publication September 23, 2019