Comparison of surrogate and subject reports of dietary practices, smoking habits and weight among married couples in the Tecumseh Diet Methodology Study.

Agreement between surrogate and subject reports of current food frequencies and other eating habits, smoking behavior and weight was assessed in 1982-1983 for 180 husbands and wives, aged 45 through 64 years. Agreement was measured by per cent exact agreement and weighted kappa for frequencies of 30 itemized foods or food groups, and for surrogate- and subject-based quintiles of frequencies of eight broad food groups and of vitamin A and C consumption indexes. Surrogate and subject mean frequencies were generally similar, but at the individual level of analysis, agreement varied widely. Agreement was greatest, among the food items and groups, for alcoholic beverages, and among the other items, for smoking status. Extreme misclassification by quintile was very small, but only 40% of persons self-classified in either extreme quintile were similarly classified by their spouses. This level of misclassification may result in the dilution of real relationships between diet and health.