The popular herbicide atrazine induces a compound that converts testosterone into estrogen. Researchers wanted to know whether the survival of some amphibian species could be at risk due to atrazine's effects on the number, function, and fertility of males. Hayes et al. (2002), researchers tested the hypothesis that atrazine reduces testosteron levels in male frogs by exposing one group of 90 male frogs to 25 parts per billion (ppb) atrazine every 3 days for 46 days. A group of 90 control males and a group of 90 contrs females were treated identically to the atrazine-treated group, except they were not exposed to atrazine. All frogs were housed individually and fed Purina rabbit chow. Aff 46 days, individual testosterone levels were measured in frogs from each group. The results are below."
What is an example of a dependent variable in this experiment?