A report on amyotrophic lateral sclerosis (ALS) found that the proportion having the disease was higher for Italian soccer players compared with the general population. The researchers suggested several explanations, none of them with certainty. For example, they speculated that therapeutic drugs may be involved, in which case it would make sense to compare rates of ALS for soccer players who do and do not use therapeutic drugs.41 Describe two groups whose data could be compared, in order to test each of the following additional possible explanations offered by the researchers:
a. Perhaps ALS is related to heavy physical exercise, and therefore not related particularly to soccer.
b. Environmental toxins like fertilizers or herbicides used on soccer fields might play a role.