Establishing reliable predictors of health behavior is a goal of health psychology. A relevant insight from personality psychology is that facets can predict specific behaviors better than broad traits do. We hypothesized that we could predict physical activity with a facet of conscientiousness related to goal pursuit-planfulness. We measured the relationship between Planfulness Scale scores and physical activity in 282 individuals over a total of 20 weeks, using a piecewise latent growth curve model. We additionally tested whether planfulness uniquely relates to activity when compared with related constructs. Finally, ratings of participants' written goals were correlated with these personality traits and physical activity. We found that planfulness was positively associated with average visits to a recreational center, that planfulness explained unique variance in activity, and that planfulness correlated with the descriptiveness of written goals. We conclude that the Planfulness Scale is a valid measurement uniquely suited to predicting goal achievement.
Keywords: goal achievement; health; open data; open materials; personality; planning; preregistered; self-regulation.