ABSTRACT. In order to obtain repeated measurements of depression in an efficient and relatively inexpensive design, a mixture of face-to-face interviews and mail questionnaires was employed. The aims of the study were to examine mode effects of face-to-face interviews versus mail questionnaires on depression scores and to test potential interactions between mode of data collection and sex and age of the respondents. In the study sample, which at the outset consisted of 327 depressed and 325 non-depressed older adults (55-85 years) drawn from a larger random community based sample in the Netherlands, depression was measured in successive waves (cycles), using the Center for Epidemiologic Studies of Depression scale (CES-D). With mode of data collection and sex and age of the respondents of the respondents as independent variables, differences in CES-D scores were analysed. The CES-D scores were higher when collected by mail questionnaires than when face-to-face interviews were used. No systematic interactions between sex and age of the respondents with mode of data collection were found. For the scores based on mail questionnaires, a transformation is proposed, resulting in scores that are comparable to those obtained by interviews. In studying depression in older adults, more cost-effective mail questionnaires may be used in addition to face-to-face interviews, provided that a transformation is performed before embarking on the analysis.
