Final answer:
Your friend should not attribute the difference in test scores to astrological signs because there are many other factors that could influence the observed differences. These factors could include the number of math courses taken, the encouragement to study certain subjects, or other potential variables that can explain the observed difference. To draw a scientifically sound conclusion, a study design would have to control for these lurking variables.
Step-by-step explanation:
Your friend should not attribute the difference in test scores to astrological signs because there are many lurking variables that could influence the observed differences. For example, the difference in test scores could be due to factors such as the number of math courses taken, the encouragement to study certain subjects, or other potential variables that can explain the observed difference. To draw a scientifically sound conclusion, a study design would have to control for these lurking variables. Therefore, it is not accurate or fair to attribute the difference solely to astrological signs.