Acognitive psychologist decides to study the effects of chess practice on math abilities in middle school students. all students are tested on a standard math test at the beginning of the study. students are then randomly assigned to a chess group and a control group. students in the chess group spend thirty minutes every school day learning chess strategy and playing chess. students in the no-chess control group spend thirty minutes every school day watching educational television. at the end of three months, students take another standardized math test. the improvement or decline in their test score is computed and compared across the two groups. in this experiment, what is the dependent variable?