R1.3: introduction should mention prior work on heterogeneity -> modelled intervention impacts

[jessexknight]

Although the authors explain why modelling key populations might influence the predicted impact of ART on HIV incidence, I think the introduction would be strengthened if they also mentioned the literature that covers heterogeneity more broadly - and the role that heterogeneity plays in determining intervention impact. For example, Nagelkerke et al (2007, BMC Infectious Diseases, 7:16) showed that the modelled impact of male circumcision on HIV incidence was much greater when assuming no heterogeneity in risk behaviour, Johnson et al (2012, Journal of the Royal Society Interface, 9:1544-54) showed that the modelled impact of condoms and ART was strongly correlated with the heterogeneity in risk behaviour, and Hontelez et al (2013, PLoS Medicine, 10:e1001534) showed that allowing for heterogeneity reduced the predicted impact of ART on HIV incidence. Key populations are one component of the heterogeneity-impact relationship, but the introduction currently reads as if they are the only determinant of the relationship.