Brian Was Playing a Game of Three Truths and a Lie

Brian was playing a game of three truths and a lie with some of his friends.The goal of the group is to identify the lie.Brian observed that the bigger the lie,the more the person would scratch his/her face.He thought that if he plotted amount of scratching by severity of lie that there would be a relation.Brian is thinking of what type of study.

A) quasi-experimental design
B) multivariate statistics
C) correlation
D) experimental design