Optimal evidence in difficult settings: improving health interventions and decision making in disasters by Gerdin, M, Clarke, M, Allen, C, Kayabu, B, Summerskill, W, Devane, D, Maclachlan, M, Spiegel, P, Ghosh, A, Zachariah, R, Gupta, S, Barbour, V, Murray, V, Von Schreeb, J