The Lancet  
Aug 06, 2011  Volume 378  Number 9790  p457 – 540
http://www.thelancet.com/journals/lancet/issue/current

Review
Mathematical models in the evaluation of health programmes
Geoffrey P Garnett, Simon Cousens, Timothy B Hallett, Richard Steketee, Neff Walker

Preview
Modelling is valuable in the planning and evaluation of interventions, especially when a controlled trial is ethically or logistically impossible. Models are often used to calculate the expected course of events in the absence of more formal assessments. They are also used to derive estimates of rare or future events from recorded intermediate points. When developing models, decisions are needed about the appropriate level of complexity to be represented and about model structure and assumptions.