A cognitive psychologist studying reading comprehension wanted to know what would happen if all college students were taught better reading strategies. She obtained a sample of 40 college students from the introductory psychology class and taught 20 of them effective reading strategies. The other 20 students were given a placebo treatment. She then gave all 40 students a standardized reading comprehension test. The mean score on the reading test for those taught the reading strategies was 49, with a standard deviation of 4 The mean score for those receiving the placebo treatment was 44, with a standard deviation of 3.8. Identi the independent variable in this study. A) scores on the reading comprchension test
B) the sample of 40 college students
C) the reading strategies class
D) the treatment group (placebo or reading strategies)