In most surveys quantitative data are gathered with questionnaires and interviews. A comparison of such self reported data with measured equivalents shows that people systematically underestimate or overestimate frequencies (cigarettes smoked daily, age of onset, time to pregnancy) or clinical parameters (height, weight, blood pressure), which may lead to misinterpretation of the association between self reported risk factors and related outcomes. Misreporting can occur because participants intentionally or unintentionally round figures to a preferred end digit. We analysed the preference forthe end digits zero and five when reporting body height in a multinational survey of individuals aged 50years and olderwho were notin institutions (12 nationally representative samples totalling 30611 valid heights, see www.share-project.org).
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