More often than not, the reason for certain patterns is multivariate. By becoming familiar with the certain methods to measure patterns and their correlation allows one to make more valid assumptions, predictions, and inference. In other words, the techniques outlined in the text provide a quantitative measure. Not always true therefore one must use caution before making inferences. For example there is a cross-correlation with Abert's tassel eared squirrel and Ponderosa pine forests.
Continuous variables change in intensity at the same time or covary.
An example may be the relationship between snowshoe hare and lynx . There numbers closely correlate with each other. Nevertheless, these types of relationships may have a lag time inherent. For example, heavy rainfall in the Texas Hill Country may cause flooding in Bastrop . The flood event usually lags behind the rainfall event.