Next: 1 Univariate Normal Distribution
Up: 2 Data Preparation
Previous: 3 Using PRELIS to
Suppose that instead of making measurements on a continuous scale, we are able
to discriminate only a few ordered categories with our measuring instrument.
This situation is commonly encountered when assessing the presence or
absence of disease, or responses to a single item on a questionnaire.
Although it is possible to calculate a covariance matrix from these data,
the correlations usually will be biased. The degree of bias depends on
factors such as the number of categories and the number of observations in each
category, and usually results in an underestimate of the true liability correlation
in the population. In this section we describe methods for summarizing ordinal
3 Ordinal Data Analysis