Data Set 4: Environmental Effects on Moth Population Growth Rates

This is an example of an analysis with several possible explanatory variables, none of which is of any special interest a priori. The purpose of the study is to determine which of these variables seems most related to the response variable, and how, in order to suggest possible causal hypotheses as well as to allow prediction. The analysis therefore aims to develop a model which explains the data well — to select apparently important variables — rather than to make formal inferences. This model building will be done in two ways: using all the data (with internal validation), and splitting the data into “training” and “validation” sets. Given the small sample size the latter method really is not appropriate but is shown to illustrate how it would be done.