Health Insurance and the Demand for Medical Care:

Evidence from a Randomized Experiment

Willard G. Manning et al. (1987)

June 1, 2007Willard G.

Question: Demand response The size of demand response Demand response and income Demand response and age group Demand response and different

services Demand response and future health

status Demand response and HMO

Problems People who face lower price use more

health care → demand response

But in reality Insurance (e.g. choices of different co-payment rate) is endogenous People who face lower price use more health

insurance People who need more use more health

insurance

Bias in the estimation

Solutions: random experiment People cannot choose what they want.

They are randomly assigned to different insurance programs

Thus No self-selection No income effect Pure moral hazard problem

Experiment Design Time:

Nov, 1974-Feb, 1977 70% for 3 years and 30% for 4 years

Observations: 5809 persons from six cities (FFS) 1982 (HMO)

Insurance: Coinsurance rate: 0, 25, 50, 95 Upper limit: 5,10,15 (income) Annual Maximum Out-pocket expense (MDE):

1000 Individual deductible – 95% coinsurance rate

for outpatient, and free for inpatient care (has upper limit)

Statistical Methods Three characteristics of distribution of

medical expenses: A large proportion use no medical services. Medical expense is highly skewed. Distribution is different between outpatient

and inpatient use Methods

ANOVA Four part equations

Four part equations

Results (I) Large medical increase when co-

payment rate moves from 25% to 0%; but a much smaller increase when moving from 95% to 50% or 50% to 25%

Total Exp (0%)~1.5 Total Exp (95%)

Results (II) EXP(In) does not change with

coinsurance rate

EXP(Out) increases significantly when coinsurance rate moves from 0 to 25%

Results (III) No large demand response on inpatient

service

U shape expenditure: probably due to the upper limit

Results (IV) Children are less responsive for

inpatient care. Adults have significant lower use of

inpatient services on the family-pay plans than on the free plan.

For other subgroups, for example, health status (healthy v.s. sick), there is no evidence to show the differential response to health insurance coverage between these two subgroups

Results (IV) Health status outcome: Patients with

relatively prevalent chronic problems (high blood pressure, myopia) have specific gains in use of free FFS rather in use plans with cost sharing.

HMO results (table 7): Same rate of using service among the

plans. The participants with one or more hospital

admissions differs with plans.

Random experiment Is it worth it? Cost: 8 millions Benefit?