Carlos, the president of a fraternity on campus, randomly sampled 500 students, asked them if they belonged to a fraternity or sorority, and asked them about their current GPA. He discovered that the GPAs of those people in fraternities and sororities were higher than those of people who were not involved in the Greek system. Gleefully, he presented his findings to the dean, saying that being involved in a fraternity or sorority leads to higher grades. What rule of research methods is Carlos breaking?

Correlation does not imply causation.

Explanation:

The rule 'correlation does not imply causation' means that just because there is a correlation between two variables it does not imply that they have cause-and-effect relationship between them.

The terms causation and correlation are oftenly used interchangeably in wrong sense of understanding.

The term correlation simply implies that there is a relationship between two variables and does not inform about hows and whys. Whereas, the term causation helps to understand the cause of change in one variable that leads to changes in another variable as well. This is also known as cause-and-effect relationship.  

The rule that Carlos is breaking in his research is that he is trying to prove a cause simply because they show a correlation between the variables. The rule of correlation does not imply causation; thus the correct answer.

you probably know the answer. stop asking stupid questions and making me waste my time. j.k. ; )   b.t.w. what are three ratios equivalent to 5 : 11? thx