For any given age group, female urinary incontinence rates varied by as much as sixfold between different population-based studies published in 1996–2011, according to a recent MEDLINE review. This finding was largely explained by variation in case definition, highlighting the need to develop standards of reporting. The authors of this review, Walter Stewart and colleagues, recommend the use of quantitative frequency criteria (such as 'twice a month') over vague thresholds (for example, 'sometimes' or 'often').