A study of the Magellanic penguin (Spheniscus magellanicus) measured stress-induced levels of the hormone corticosterone in chicks living in either tourist-visited areas or undisturbed areas of a breeding colony in Argentina (Walker et al. 2005). Chicks at three stages of development were included in the study—recently hatched, midway through growth, and close to fledging. Penguin chicks were stressed by being captured by the researchers and their corticosterone concentrations were measured 30 minutes later. The following graph diagrams the mean hormone concentrations for the three age groups of chicks from tourist-visited (filled circles) and undisturbed (open circles) areas of the colony.

a. What is the response variable?

b. What are the explanatory variables?

c. The line segments in this plot are not parallel. What does this suggest?

d. Is this an observational or experimental study Explain.

e. Did the study use a factorial design? Explain.