Wiley's study described the achievement test scores and reading grades of a cross-sectional sample of elementary school students. He took the students' scores on an achievement test and divided the students into three groups based on their scores: high, medium, and low. He then described the reading scores of the students in the three groups. Why did he do this? Group of answer choices to turn his study into an experiment by having a categorical independent variable because every research study has to have a categorical variable to create a categorical variable from a quantitative variable to create a quantitative variable from a categorical variable