EXAMPLE 8 SAT scores and college grades

High scores on the SAT examinations in high school certainly do not cause high grades in college. The moderate association ( is about 27%) is no doubt explained by common response variables such as academic ability, study habits, and staying sober. Figure 15.5(b) illustrates this. In the figure, might correspond to academic ability, to SAT scores, and to grades in college.

The ability of SAT scores to partly predict college performance doesn’t depend on causation. We need only believe that the relationship between SAT scores and college grades that we see in past years will continue to hold for this year’s high school graduates. Think once more of our fossils, where femur length predicts humerus length very well. The strong relationship is explained by common response to the overall age and size of the beasts whose fossils we now examine. Prediction doesn’t require causation.