Hatzigeorgiadis et al. 2011, Self-talk and sports performance, a meta-analysis

Meta-analysis of 32 studies (62 effect sizes) of self-talk interventions in sport. Self-talk produced a positive moderate overall effect on performance (ES about 0.48), larger for fine and novel tasks; instructional self-talk outperformed motivational self-talk specifically for fine motor tasks. The effect is real but heterogeneous and moderated by task type. Moderate.