$1\mathrm{.}4$

Because of a recent increase in the number of neck injuries incurred by high school football players, the Department of Commerce designed a study to evaluate the strength of football helmets worn by high school players in the United States. A total of $540$ helmets were collected from the five companies that currently produce helmets. The agency then sent the helmets to an independent testing agency to evaluate the impact cushioning of the helmet and the amount of shock transmitted to the neck when the face mask was twisted.

a$.$ What is the population of interest?

b$.$ What is the sample?

c$.$ What variables should be measured?

d$.$ What are some of the major limitations of this study in regard to the safety of helmets worn by high school players? For example, is the neck strength of the player related to the amount of shock transmitted to the neck and whether the player will be injured?