Naturally, the question arises if selection plays a role: Perhaps, the most productive, ambitious postdocs stay in academia, while others leave with no wage premium or loss. Apart from including a set of control variables that can account for the difference between doctoral graduates, Johannes uses a matching approach that shall partially reduce this concern. He matches statistically comparable doctoral graduates on observable characteristics, e.g., age, citizenship, previous work experience, and compares the wages among them. Yet, the pattern remains unchanged after this procedure suggesting the robustness of the observed wage gap.
These results beg the question if one can consider the postdoctoral period as a further qualification used to justify a postdoc's relatively insecure working conditions. Why is the payoff so low if the postdoctoral period is deemed the advanced qualification phase?
König, J., 2022. Postdoctoral employment and future non-academic career prospects. Plos one, 17(12), p.e0278091.