Suppose that a fellow student comes to you with the following idea for how to estimate marginal returns to medical care: within a group of patients, regress mortality on health spending. She does so and finds a positive coefficient. Which of the following is NOT a strong explanation for her findings?

Group of answer choices

a. health spending increases mortality AND sicker patients have higher healthspending

b. health spending reduces mortality AND sicker patients have lower health spending

c. health spending has no impact on mortality AND sicker patients have higher health spending

d. health spending reduces mortality, BUT that impact is obscured because sicker patients have higher health spending