In the 1980s and 1990s many states passed Any-Willing-Provider (AWP) legislations that require managed care organizations to accept any provider into their network if the provider agrees to the conditions, terms and reimbursement rates. Suppose you are hired by an agency to estimate the effect of AWP legislation on state-level hospital and physician expenditures (EXP). You have state-level data on expenditures, year AWP law passed, and demographic and health characteristics spanning 1980 through 1998. Note that both EXP and AWP vary across years and states. The state-level demographic and health characteristics include population density, percent of the population of African American race, HMO market share, real per capita income and unemployment rate. Assume that data are available for 50 states. A. What approach would you use to estimate the effect of the policy change (i.e., AWP) on total hospital and physician expenditures? Specify your model (the equation and important assumptions), and then explain your estimation approach