Like the comparison of key research themes that appeared in JAP and PPsych over the 45year period of the review, there is also considerable overlap in key human capital themes within decades. We do not elaborate these, however, because our purpose in this section is to examine the correspondence between key themes in published research and human capital trends. Let us begin by focusing on lagged relationships, with the caveat that because we did not implement an experimental design, we cannot make inferences about causality (i.e., whether a particular human capital trend did, in fact, cause a particular publication trend).