ABSTRACT Fixed effects (FE) have emerged as a ubiquitous and powerful tool for eliminating unwanted variation in observational accounting studies. Unwanted variation is plentiful in accounting research because we often use rich data to test precise hypotheses derived from abstract theories. By eliminating unwanted variation, FE reduce concerns that omitted variables bias our estimates or weaken test power. FE are not costless, though, so their use should be carefully justified by theoretical and institutional considerations. FE also transform samples and variables in ways that are not immediately apparent, and in doing so affect how we should interpret regression results. This primer explains the mechanics of FE and provides practical guidance for the informed use, transparent reporting, and careful interpretation of FE models.

ABSTRACT We examine the effects of stock market access, and in particular trading hours, on retail investment performance. Using discontinuities around time zone borders, we find that plausibly exogenous decreases in waking trading hours are associated with meaningful increases in retail investors’ capital gains, as reported on tax returns for the U.S. population. Our results indicate that limiting trading hours curbs active retail trading, leading to improvements in portfolio performance. Our findings identify one negative effect of decreasing barriers to entry for retail investors in trading markets. JEL Classifications: M41; M48; G40; G51.