Do the following data come from an experiment or an observational study?A gene 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 from three 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 study1 suggests that sprinters are less likely than non-sprinters to have the gene variant.