Background: The objective of this study was to assess the agreement and repeatability of 2 methods of measuring habitual coffee consumption, and to examine their homogeneity with respect to socioeconomic and lifestyle factors.
Methods: Data on coffee consumption were collected from 4254 subjects by means of a health questionnaire (HQ) and a 1-year dietary history interview (DHI), the latter of which was used as the reference method during the Finnish Mobile Clinic Health Examination Survey conducted in 1973-1976. Short-term repeatability of the methods was assessed using data from 286 and 93 subjects who repeated the HQ and the DHI, respectively, after an interval of 4 to 8 months. The strength of agreement between the 2 methods and between the repeated measurements was estimated using intraclass correlation coefficients (ICCs).
Results: The ICC was 0.86 for the agreement between the HQ and the DHI, and 0.77 and 0.85 for the repeatability of the HQ and the DHI, respectively. There were no statistically significant systematic differences in mean intake values between the 2 methods or between repeated measurements. In subgroup analysis of background variables, there were only minor differences in agreement and repeatability, with somewhat higher ICC values among subjects with a healthier lifestyle and higher education.
Conclusions: The high reliability and homogeneity of the health questionnaire make it a useful tool for measuring habitual coffee consumption for the purposes of epidemiological research.