For malaria Keiser et al. reviewed environmental measures aimed at reducing disease transmission [46]. They identified 40 studies, of these, 27 assessed effects of environmental modification such as drainage, filling-in ponds and pools and river boundary modification. Four studies assessed effects of environmental manipulation (e.g. intermittent irrigation) and 9 modification or manipulation of human habitation (e.g. mosquito proofing homes). The reviewers reported significant heterogeneity and evidence of publication bias but presented the results of meta-analyses and concluded “malaria control programmes that emphasise environmental management are highly effective in reducing morbidity and mortality”. The authors took little account of study quality, stating that it was impossible to scrutinise the methodological quality as most studies were implemented 50–100 years ago. GRADE assessment suggested the quality of evidence was moderate for environmental manipulation and very low for the other intervention types, methodological issues included use of historical controls (before-after studies) in many studies and not accounting for possible confounding factors (additional treatments or personal protection interventions). The authors' conclusion that environmental management is highly effective in reducing morbidity and mortality is not substantiated by the evidence. A further high quality review of the evidence would be helpful before commissioning further primary research in this area.