Dichotomous or categorical response? Analysing self-rated health and lifetime social class.

BACKGROUND Self-rated health is a commonly used measure of health status, usually having three to five categories. The measure is often collapsed into a dichotomous variable of good versus less than good health. This categorization has not yet been justified. METHODS Using data from the 1958 British birth cohort, we examined the relationship between socioeconomic conditions, indicated by occupational class at four ages, and self-rated health. Results obtained for a dichotomous variable using logistic regression were compared with alternative methods for ordered categorical variables including polytomous regression, cumulative odds, continuation ratio and adjacent categories models. RESULTS AND CONCLUSIONS Findings concerning the relationship between socioeconomic position and self-rated health yielded by a logistic regression model were confirmed by alternative statistical methods which incorporate the ordered nature of self-rated health. Similarity of results was found regarding size and significance of main effects, type of association and interactive effects.