Simple Inference for Categorical Data: From Sandflies to Organic Particulates in the Air
We will first demonstrate how raw data may be put into the form of a crossclassification using the data on mortality and water hardness from the previous chapter.
The raw data are read into a SAS data set, water, as described in the previous chapter. In this instance, two new variables are computed – mortgrp and hardgrp – which dichotomize mortality and water hardness at their medians. Strictly speaking, the expression mortal> 1555 is a logical expression yielding the result ‘‘true’’ or ‘‘false,’’ but in SAS these are represented by the values 1 or 0, respectively.