A research team wants to estimate the effectiveness of a new veterinary drug for sick seals. They ask aquariums across the country to volunteer their sick seals for the experiment. Since the team offers monetary compensation for volunteering, zoos with less income decide to volunteer their sick seals, whereas zoos with more income are less compelled to volunteer their seals. It turns out that zoos with less income feed their seals less nutritious diets (regardless of whether they are sick or healthy), due to budgetary constraints. Less nutritious diets prevent seals from recovering as effectively