OBJECTIVES: Clinical study results might be substantially biased by the effects of ageing, resulting in considerable underestimation of treatment efficacy, especially when assessing activities of daily living (ADL) in elderly people. This study aimed to define age- and comorbidity-related normative values in ADL. METHODS: In cross-sectional sampling, 23 763 German-speaking Swiss individuals were contacted. Valid questionnaires from 16 191 (68%) eligible individuals ≥ 18 years of age were included in the study. Age-related ADL reference values were calculated using questionnaire data. RESULTS: The sample was representative of the German-speaking Swiss population as determined by 2003 census data. Age- and pain-related ADL reference values were plotted and confirmed that disability increased with increasing age. CONCLUSIONS: The use of ADL scales that provide age- and comorbidity-related reference values for outcome studies or studies focusing on the elderly is recommended in order to reduce the effect of bias.
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