Answer to Question #281886 in Genetics for Picklerabbit

Question

The correlation coefficient is a measure of the strength of association between two traits. Correlation, however, does not indicate causation (interconnection). Think of one or two variables (not necessarily phenotypes) that are correlated and are causally linked, and one or two variables that may be correlated but are not likely to be causally linked.

Answer 1

An example of a variable that is correlated and is causally linked ; consider the positive correlation between the number of hours you spend studying for a test and the grade you get on the test. Here, there is causation as well; if you spend more time studying, it results in a higher grade.

An example of a variable that may be correlated but are not likely to be causally linked ; being a patient in hospital is correlated with dying, but this does not mean that one event causes the other, as another third variable might be involved such as diet.