Effect of different factors on the estimated statistical power to detect a pre-erythrocytic immune response that prevents 50% of infections for the study designs identified in the systematic review. (A) Studies reporting statistically significant associations had higher estimated power than studies not reporting significant associations. (B) Studies of antibody responses had greater estimated power than studies of cellular responses. (C) Large studies (≥100 participants) had greater estimated power than small studies (< 100 participants). (D) Studies undertaken in high transmission settings (≥10 ibppy) had greater estimated power than studies undertaken in low transmission settings (< 10 ibppy). (E) Studies where the immune response was analysed as a binary variable had greater estimated statistical power than studies where responses were analysed as continuous variables. This result can be explained by the fact that studies with binary immune responses had larger numbers of participants than studies with continuous immune responses. (F) Studies with longitudinal follow up with active detection of infection (ADI) had greater estimated power than studies without ADI.