Figure 1. Example of a notable difference between one-stage and two-stage IPDMA results, as reported by Martineau et al.³¹ who synthesise IPD from 25 randomised controlled trials (10,933 participants) to examine whether Vitamin D supplementation prevented acute respiratory tract infections. Case study and figure originally shown by Riley et al.²⁹ [Colour figure can be viewed at wileyonlinelibrary.com].