Objective To identify methods to increase response to postal questionnaires. Design Systematic review of randomised controlled trials of any method to influence response to postal questionnaires. Studies reviewed 292 randomised controlled trials including 258 315 participants Intervention reviewed 75 strategies for influencing response to postal questionnaires.

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms SummaryThis review is intended to help clinicians, patients and the public make informed decisions about statin therapy for the prevention of heart attacks and strokes. It explains how the evidence that is available from randomized controlled trials yields reliable information about both the efficacy and safety of statin therapy. In addition, it discusses how claims that statins commonly cause adverse effects reflect a failure to recognise the limitations of other sources of evidence about the effects of treatment.Large-scale randomized trial evidence shows that statin therapy reduces the risk of heart attacks, ischaemic strokes and coronary revascularization procedures ("major vascular events") by about one quarter for each mmol/L reduction in low density lipoprotein (LDL) cholesterol during each year (after the first) that it continues to be taken. The absolute benefits of statin therapy depend on an individual's absolute risk of occlusive vascular events and the absolute reduction in LDL cholesterol that is achieved. For example, lowering LDL cholesterol by 2 mmol/L (77 mg/dL) with an effective low-cost statin regimen (e.g. atorvastatin 40 mg daily, costing about £2 per