For example, meta-analysis of surrogate outcome studies (Buyse et al., 2000; Michiels et al., 2009; Daniels and Hughes, 1997; Gail et al., 2000; Buyse, 2009), where a primary aim is to estimate and use the correlation between a surrogate outcome and a true outcome (such as between CD4 count and AIDS); prognostic studies where the absolute survival risk at multiple time points is needed (Arends et al., 2008); and investigations of the association between treatment effect and baseline risk (Van Houwelingen et al., 2002; Senn, 2010; Van Houwelingen et al., 1993). Here, CD4 is linked to AIDS.