THE GENERALIZATION OF PROBIT ANALYSIS TO THE CASE OF MULTIPLE RESPONSES

The generalized probit analysis which we will discuss in this paper arose from a problem in entomology. We will suggest a solution to this particular problem and then consider a more general situation where this method of solution might be appropriate. The particular problem is as follows. In the course of its lifetime the Petrobius Leach (Thysanura, Machilidae), which is a primitive wingless insect allied to the domestic silverfish, passes through various stages, technically referred to as 'instars'. A problem of biological interest is to estimate the mean time spent by such insects in each instar (stage). Since there are difficulties involved in keeping these insects alive in the laboratory (and consequently in keeping them under effectively continuous observation during their lifetime), they were sampled at various dates in the field, and those observed were classified according to instar. The actual set of data to be analysed is given in Table 1.* The insects started hatching on 30 April and times will be measured from this date. The problem is to estimate from these data the mean time spent in each stage.