A regression method for analysing ordinal data from intervention trials.

Abstract

We consider the case of a community intervention trial evaluated with a series of cross-sectional surveys and having outcomes measured on an ordinal scale. We propose a modelling procedure that combines ridit analysis and linear regression methods. We use the multinomial distribution as the basis for variance estimation of the mean ridits and then use simple regression models to estimate differences (for example, between intervention and comparison areas) among the ridits. We illustrate this procedure with data from a community intervention trial promoting condom use, with the adoption of consistent condom use measured on a 5-point ordinal scale.