Spurling et al. investigated the effects of two vocabulary learning strategies on word retention two weeks later. in this example, learning strategy is the variable and word retention is the variable.

Learning strategy is the independent variable and word retention is the dependent variable.

A dependent variable is the thing that is being measured or tested by changes in the independent variable. Spurling wanted to test how word retention depended on different learning strategies.

Learning strategy is independent variable here and word retention is dependent variable.

Explanation:

An independent variable is a variable that is not affected by changes in the other variable in a test or experiment, and dependent variable is the one which is to be tested by making changes in the independent variable. So here, Spurling et al. has taken word retention as dependent variable because he wanted to test the effect of different learning strategies on the word retention in the scope of vocabulary.