Dorothy is testing the effect of age on basic math skills. She recruits 300 students from School A and 300 students from School B. The School A students are 11 years old, and the School B students are 12 years old. All students complete the same standardised math test that has been well validated and is reliable. Higher scores indicate higher basic math skills. She statistically compares the performance of the 11-year-old student group to the performance of the 12-year-old student group and finds a difference. The 11-year-old group performs better than the 12-year-old group as they have a relatively higher mean score on the standardised math test. Dorothy concludes that age influences math skills: the younger the student, the better their math skills. Which option best describes why Dorothy might have come to an incorrect conclusion? Group of answer choices She did not empirically observe the results of her study She has failed to rule out an alternative explanation for the results She has not measured any variables in her study She has collected data from a population rather than from a sample