Sixth, we focused on the effect of participant age on the outcomes of interest. We controlled for linear differences in time lag, but it is also possible that stability decays in a nonlinear manner as more time passes between assessments toward some lower asymptote. As a sensitivity analysis (not presented), we included a quadratic time lag term in each of the continuous exponential models. This addition did not substantively change any of the lifespan trends, and the quadratic term tended to be small in magnitude.8 Although the current article was specifically focused on age-based lifespan trends in stability, it will be valuable for future research to examine time-based trends in stability. This analysis will help to determine the most appropriate functional form of stability decay, and whether such decay interacts with the age of the participants (e.g., stability may fall precipitously at early ages, but persist through time in adulthood).
