The dependent variable is simply that; a variable that is dependent on an independent variable(s). In our case, the test mark (. the dependent variable) that a student achieves is dependent on revision time and intelligence (., the independent variables). Whilst revision time and intelligence (., independent variables) may (or may not) cause a change in the test mark (., the dependent variable), the reverse is implausible. In other words, whilst the number of hours a student spends revising and the higher a student's IQ score may (or may not) change the test mark that a student achieves, a change in a student's test mark has no bearing on whether a student revises more or is more intelligent. This would not make any sense.