Data collected by survey methodology are sensitive to measurement errors. Factors of memory, understanding, and willingness to respond truthfully, distort the quality of results. In this paper, time diaries were used as a quality check for results obtained by direct interviews and questionnaires. Data is based on surveys carried out by Statistics Finland. Comparison showed that measurement error varied considerably between population groups, influencing dependencies and interpretations of the results. Activities clearly distinctive from other activities, such as gainful employment outside the home, produced the most accurate data in direct survey questions. Everyday activities that don't clearly stand out from other uses of time, such as home based employment, are difficult to recall and produce a lot of biasing measurement errors.