Correlation, causation, motivation, and second language acquisition.

Abstract

It is well known to anyone who has taken even an introductory course in statistics that does not mean causation. This is a truism! The present article examines four truisms about correlation, demonstrating that they are not always true. For example, under certain conditions, correlation can imply causation, though these conditions are seldom satisfied in most applications. Nonetheless, there are many of us who are interested in investigating individual differences, and in making inferences of the type that this individual difference variable is related to, mediates, moderates, or even causes or influences that individual difference variable. Generally speaking, the analytic procedures we use involve the correlation coefficient in one form or another. I propose four steps that researchers can follow to accumulate evidence that increases one's confidence in the validity of a particular causal model. These steps are illustrated by reviewing research on individual differences in second language acquisition. This approach is not conclusive, of course, but it does force one to examine the implications of the model, thus leading to further insights and research. Although the focus here is on second language acquisition, the generalizations apply to other areas of research that are concerned with individual differences.