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essays in public finance and industrial organization a dissertation ...

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CHAPTER 2. HEALTH PLAN CHOICE 82<br />

2.4.2 Discussion of Model <strong>and</strong> Identification<br />

The key quantities <strong>in</strong> our model are plan costs <strong>and</strong> plan dem<strong>and</strong> as functions of fore-<br />

castable risk, <strong>and</strong> the price elasticity of dem<strong>and</strong>. The former determ<strong>in</strong>e the efficient<br />

allocation of households to plans, while the latter determ<strong>in</strong>es how price changes affect<br />

self-selection. We now discuss the variation <strong>in</strong> the data that identifies each of these<br />

quantities <strong>in</strong> estimation.<br />

Identify<strong>in</strong>g plan costs is straightforward. The effect of forecastable risk on plan<br />

costs is identified by variation across firms <strong>in</strong> the average risk scores of workers <strong>and</strong><br />

dependents, <strong>and</strong> how it affects <strong>in</strong>surer bids <strong>and</strong> realized costs. We identify the mark-<br />

up parameters, δj, by the difference between the plan bids <strong>and</strong> reported costs. A<br />

ma<strong>in</strong>ta<strong>in</strong>ed assumption <strong>in</strong> estimat<strong>in</strong>g mark-ups is that <strong>in</strong>surers base their bids on<br />

only the <strong>in</strong>formation about employees that is provided by the <strong>in</strong>termediary. We<br />

discuss this assumption more below, but we believe it is reasonable given the small<br />

size of the contracts <strong>and</strong> the fact that we consider only the first year of plan bids.<br />

The effect of household risk on choice behavior (i.e. the coefficients αrj <strong>in</strong> the<br />

dem<strong>and</strong> equation) is identified by variation <strong>in</strong> observable risk across households. Our<br />

model also allows private <strong>in</strong>formation about health status to affect choice. The key<br />

parameter here is the variance of the private <strong>in</strong>formation, σ 2 µ, which is identified by<br />

the correlation between consumers’ enrollment decisions <strong>and</strong> plans’ realized costs.<br />

This identification is aided by cross-firm variation <strong>in</strong> contribution policies <strong>and</strong> demo-<br />

graphics that, conditional on observable health risk, affect enrollment but not realized<br />

costs. 17 The identification obta<strong>in</strong>ed from price variation is similar to the identifica-<br />

tion <strong>in</strong> st<strong>and</strong>ard selection models, <strong>and</strong> relies on the exclusion restriction if a given<br />

<strong>in</strong>dividual i is enrolled <strong>in</strong> a given plan j, his or her utilization does not depend on<br />

the per-month premium (although of course it may depend on other elements of the<br />

plan such as the copayment rate).<br />

The most subtle identification issues arise <strong>in</strong> estimat<strong>in</strong>g the effect of plan con-<br />

tributions on dem<strong>and</strong>. Plan contributions are the result of plan bids <strong>and</strong> employer<br />

pass-through decisions. Our model allows four sources of variation <strong>in</strong> contributions:<br />

17 Our dem<strong>and</strong> model also <strong>in</strong>cludes plan characteristics such as co<strong>in</strong>surance <strong>and</strong> deductible. Their<br />

coefficients are identified off cross-firm <strong>and</strong> cross-tier variation <strong>in</strong> the characteristics.

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