Medicaid Expansion Medicaid is a program administered by the states that provides medical help to low-income residents. Read the extract given, and then answer the questions that follow it.

(Source: Sommers et al., Mortality and access to care among adults after state Medicaid expansions, New England Journal of Medicine, vol. 367: 1025-1034, July 25, 2012) Methods We compared three states that had substantially expanded adult Medicaid eligibility since 2000 (New York, Maine, and Arizona) with neighboring states that had not enacted such expansions. The sample consisted of adults between the ages of 20 and 64 years who were observed 5 years before and 5 years after the expansions, from 1997 through 2007.

The primary outcome was all-cause county-level mortality rates.... Results Medicaid expansions were associated with a significant reduction in adjusted all-cause mortality (by 19.6 deaths per 100,000 adults, for a relative reduction of 6.1%; P = 0.001). Mortality rate reductions were greatest among older adults, nonwhites, and residents of poorer counties.... Medicaid expansions increased rates of self-reported health status of "excellent" or "very good" (by 2.2 percentage points, for a relative increase of 3.4%; P = 0.04).

a. Identify the treatment variable and the response variable.

b. Was this a controlled experiment or an observational study? Explain

c. Can you conclude that the increase in Medicaid caused the good results? Why or why not?