A researcher was interested in comparing the effectiveness o…
A researcher was interested in comparing the effectiveness of 3 types of instructional materials for teaching 1 biology concept. The instructional materials included: using text materials, video materials, text + video materials. 25 10th grade Biology students were randomly assigned to each type of instructional material for a total of 75 students. These 75 students were volunteers recruited from an after-school program. Students used the method for 1, 2-hour session and were then tested using a 20 item Biology exam. The researcher used random assignment. List 1 other method the researcher could use to control and reduce extraneous and confounding variables?