"Is there a sprinting gene?" Introduced in Example 1.5. Indicate whether the data come from an experiment or an observational study.

Data From Example 1.5:

Is There a “Sprinting Gene”?
Agene called ACTN3 encodes a protein which functions in fast-twitch muscles. Some people have a variant of this gene that cannot yield this protein. (So we might call the gene variant a possible non-sprinting gene.) To address the question of whether this gene is associated with sprinting ability, geneticists tested people fromthree different groups: world-class sprinters, world-class marathon runners, and a control group of non-athletes. In the samples tested, 6% of the sprinters had the gene variant, compared with 18% of the non-athletes and 24% of the marathon runners. This study4 suggests that sprinters are less likely than non-sprinters to have the gene variant.

(a) What are the cases and variables in this study? Indicate whether each variable is categorical or quantitative.

(b) What might a table of data look like for this study? Give a table with a possible first two cases filled in.