Overview of Methodology for Imputing 

Missing Expenditure Data in the Medical 

Expenditure Panel Survey 

Agency for Healthcare Research and Quality 

U.S. Department of Health & Human Services March 2007 
ABSTRACT

In the Medical Expenditure Panel Survey (MEPS), expenditures are defined as

payments from all sources (including individuals, private insurance, Medicare, 

Medicaid, and other sources) for health care services during the year. Data on

expenditures are collected for sample persons in the Household Component of the 

survey and from a sample of their health care providers responding to the Medical 

Provider Component of the survey. In the absence of payment information from

either component, expenditure data are completed through weighted hot-deck 

imputation procedures. The MEPS collects a wide variety of data about individuals and health care events that are correlated with expenditures and, for each

event type (e.g., doctor visits, hospitalizations, etc.), a selected set of these 

variables is used in the imputation processes. Several hot-deck iterations are run 

for each medical event type category based on factors such as whether partial 

payment information was reported and whether payments for the event covered 

multiple visits. This paper provides an overview of the methodological approach

to impute MEPS expenditure data and how class variables for the hot-deck 

procedures were determined. 

Suggested Citation: 

Machlin, S. R. and Dougherty, D. D. Overview of Methodology for Imputing

Missing Expenditure Data in the Medical Expenditure Panel Survey. Methodology Report No. 19. March 2007. Agency for Healthcare Research and Quality,

Rockville, Md. http://www.meps.ahrq.gov/mepsweb/data_files/publications/ 

mr19/mr19.pdf 

∗ ∗ ∗

The estimates in this report are based on the most recent data available at the time 

the report was written. However, selected elements of MEPS data may be revised 

on the basis of additional analyses, which could result in slightly different 

estimates from those shown here. Please check the MEPS Web site for the most 

current file releases. 

Center for Financing, Access, and Cost Trends 

Agency for Healthcare Research and Quality

540 Gaither Road 

Rockville, MD 20850 

www.meps.ahrq.gov

ii
The Medical Expenditure Panel Survey (MEPS) 

Background 

The Medical Expenditure Panel Survey (MEPS) is conducted to provide nationally

representative estimates of health care use, expenditures, sources of payment, and 

insurance coverage for the U.S. civilian noninstitutionalized population. MEPS is 

cosponsored by the Agency for Healthcare Research and Quality (AHRQ), formerly the 

Agency for Health Care Policy and Research, and the National Center for Health 

Statistics (NCHS). 

MEPS comprises three component surveys: the Household Component (HC), the 

Medical Provider Component (MPC), and the Insurance Component (IC). The HC is the

core survey, and it forms the basis for the MPC sample and part of the IC sample. 

Together these surveys yield comprehensive data that provide national estimates of the 

level and distribution of health care use and expenditures, support health services 

research, and can be used to assess health care policy implications. 

MEPS is the third in a series of national probability surveys conducted by AHRQ on the 

financing and use of medical care in the United States. The National Medical Care

Expenditure Survey (NMCES) was conducted in 1977, the National Medical 

Expenditure Survey (NMES) in 1987. Beginning in 1996, MEPS continues this series 

with design enhancements and efficiencies that provide a more current data resource to 

capture the changing dynamics of the health care delivery and insurance system. 

The design efficiencies incorporated into MEPS are in accordance with the Department 

of Health and Human Services (DHHS) Survey Integration Plan of June 1995, which 

focused on consolidating DHHS surveys, achieving cost efficiencies, reducing 

respondent burden, and enhancing analytical capacities. To accommodate these goals, 

new MEPS design features include linkage with the National Health Interview Survey

(NHIS), from which the sample for the MEPS-HC is drawn, and enhanced longitudinal 

data collection for core survey components. The MEPS-HC augments NHIS by selecting 

a sample of NHIS respondents, collecting additional data on their health care 

expenditures, and linking these data with additional information collected from the 

respondents’ medical providers, employers, and insurance providers. 

Household Component 

The MEPS-HC, a nationally representative survey of the U.S. civilian noninstitutionalized population, collects medical expenditure data at both the person and household 

levels. The HC collects detailed data on demographic characteristics, health conditions, 

health status, use of medical care services, charges and payments, access to care, 

satisfaction with care, health insurance coverage, income, and employment. 

The HC uses an overlapping panel design in which data are collected through a 

preliminary contact followed by a series of five rounds of interviews over a two and a 

half year period. Using computer-assisted personal interviewing (CAPI) technology, data 

on medical expenditures and use for two calendar years are collected from each

household. This series of data collection rounds is launched each subsequent year on a 

new sample of households to provide overlapping panels of survey data and, when 

iii
combined with other ongoing panels, will provide continuous and current estimates of

health care expenditures. 

The sampling frame for the MEPS-HC is drawn from respondents to NHIS, conducted

by NCHS. NHIS provides a nationally representative sample of the U.S. civilian 

noninstitutionalized population, with oversampling of Hispanics and blacks. 

Medical Provider Component 

The MEPS-MPC supplements and validates information on medical care events reported 

in the MEPS-HC by contacting medical providers and pharmacies identified by household respondents. The MPC sample includes all hospitals, hospital physicians, home 

health agencies, and pharmacies reported in the HC. Also included in the MPC are all 

office-based physicians:

 Providing care for HC respondents receiving Medicaid. 

 Associated with a 75 percent sample of households receiving care through an HMO 

(health maintenance organization) or managed care plan. 

 Associated with a 25 percent sample of the remaining households. Data are collected 

on medical and financial characteristics of medical and pharmacy events reported by

HC respondents, including: 

 Diagnoses coded according to ICD-9 (9th Revision, International Classification of 

Diseases) and DSMIV (Fourth Edition, Diagnostic and Statistical Manual of Mental

Disorders). 

 Physician procedure codes classified by CPT-4 (Current Procedural Terminology, 

Version 4). 

 Inpatient stay codes classified by DRG (diagnosis related group). 

 Prescriptions coded by national drug code (NDC), medication names, strength, and 

quantity dispensed. 

 Charges, payments, and the reasons for any difference between charges and 

payments. 

The MPC is conducted through telephone interviews and mailed survey materials. 

Insurance Component 

The MEPS-IC collects data on health insurance plans obtained through private and 

public sector employers. Data obtained in the IC include the number and types of private 

insurance plans offered, benefits associated with these plans, premiums, contributions by

employers and employees, and employer characteristics. 

Establishments participating in the MEPS-IC are selected through three sampling 

frames: 

 A list of employers or other insurance providers identified by MEPS-HC respondents 

who report having private health insurance at the Round 1 interview. 

 A Bureau of the Census list frame of private-sector business establishments. 

 The Census of Governments from the Bureau of the Census. 

To provide an integrated picture of health insurance, data collected from the first 

sampling frame (employers and other insurance providers) are linked back to data

provided by the MEPS-HC respondents. Data from the other three sampling frames are 

collected to provide annual national and State estimates of the supply of private health 

iv
insurance available to American workers and to evaluate policy issues pertaining to 

health insurance. Since 2000, the Bureau of Economic Analysis has used national 

estimates of employer contributions to group health insurance from the MEPS-IC in the 

computation of Gross Domestic Product (GDP). 

The MEPS-IC is an annual panel survey. Data are collected from the selected

organizations through a prescreening telephone interview, a mailed questionnaire, and a 

telephone follow-up for nonrespondents. 

Survey Management 

MEPS data are collected under the authority of the Public Health Service Act. They are 

edited and published in accordance with the confidentiality provisions of this act and the

Privacy Act. NCHS provides consultation and technical assistance. 

As soon as data collection and editing are completed, the MEPS survey data are released 

to the public in staged releases of summary reports and microdata files. Summary reports 

are released as printed documents and electronic files. Microdata files are released on 

CD-ROM and/or as electronic files.

Printed documents and CD-ROMs are available through the AHRQ Publications 

Clearinghouse. Write or call: 

AHRQ Publications Clearinghouse 

Attn: (publication number) 

P.O. Box 8547 Silver Spring, MD 20907 

800-358-9295 

703-437-2078 (callers outside the United States only)

888-586-6340 (toll-free TDD service; hearing impaired only) 

To order online, send an e-mail to: ahrqpubs@ahrq.gov. 

Be sure to specify the AHRQ number of the document or CD-ROM you are requesting. 

Selected electronic files are available through the Internet on the MEPS Web site: 

http://www.meps.ahrq.gov/

For more information, visit the MEPS Web site or e-mail mepspd@ahrq.gov. 

v
Table of Contents

Introduction ..................................................................................................................... 1

MEPS Sample Design...................................................................................................... 1

MEPS Expenditures Defined ........................................................................................... 2

MEPS Household Expenditure Data Collection............................................................... 2

MEPS Expenditure Estimation Strategy .......................................................................... 3

Imputation Process .......................................................................................................... 4

Summary ......................................................................................................................... 6

References....................................................................................................................... 6

Acknowledgments........................................................................................................... 7

vi
Overview of Methodology for Imputing Missing Expenditure 

Data in the Medical Expenditure Panel Survey

Steven R. Machlin, Agency for Healthcare Research and Quality, and Deborah D. 

Dougherty, Westat

Introduction 

The Medical Expenditure Panel Survey (MEPS) is a complex national probability survey

of the U.S. civilian noninstitutionalized population, and has been conducted on an annual 

basis since 1996 by the Agency for Healthcare Research and Quality (AHRQ). One of

the primary purposes of the survey is to collect data that can be used to analyze national 

medical expenditures (i.e., the amount paid for health care services). 

Unfortunately, it is difficult to obtain complete information on medical expenditures 

from household survey respondents because the type of information being collected is 

often not straightforward and requires extensive record keeping over time, especially for 

households with members who frequently use the health care system. Further, in a 

significant number of instances, respondents are simply not aware of either the total 

amount billed or how much the provider is paid for the services that were received. 

Classic examples are individuals enrolled in the Medicaid program, where financial 

transactions occur only between the provider and the state Medicaid agency, and 

enrollees of managed care plans or HMOs who only may be aware of paying some 

predetermined co-payment that is not necessarily related to the total amount the provider 

receives (Cohen et al., 1997). 

As a consequence of these factors, there is a substantial amount of item nonresponse on 

medical expenses in the Household Component (HC) of MEPS. To compensate for these 

missing data and to improve accuracy, data on expenses for sample persons are also 

collected from a sample of their health care providers in the Medical Provider 

Component (MPC) of MEPS (see description of MPC under MEPS Expenditure 

Estimation Strategy below). However, expense data are not available from either survey

component for a noteworthy proportion of medical events reported in the survey (e.g., 

roughly one-third in 2001). 

A weighted hot-deck approach is used to impute missing expenditure data in MEPS. 

This approach uses other survey responses to complete missing data and incorporates

survey weights to replicate the weighted distribution of the available data in the imputed 

data (Cox, 1980). The objectives of the imputations are to create data sets for analysis 

that preserve sample sizes and reduce the potential for nonresponse bias in analyses of

MEPS expenditure data. This paper provides a general overview of the MEPS 

expenditure imputation process. 

MEPS Sample Design 

The sample of households for the MEPS-HC is a subsample of households that 

responded to the prior year’s National Health Interview Survey (NHIS) conducted by the 

National Center for Health Statistics (National Center for Health Statistics, 2002). The 

MEPS sample is drawn from approximately half of the primary sampling units (PSUs) 

selected for the NHIS. For example, the 1996 MEPS-HC sample was selected from 

1
households that responded to the 1995 NHIS (Cohen S., 1997). This selection was 

comprised of 195 PSUs and 1,675 sample segments (second-stage sampling units). Over 

sampling of households with Hispanics and blacks carries over from the NHIS to the 

MEPS sample design. 

The sample design of the Medical Expenditure Panel Survey is an overlapping panel 

design, with data collected for each new MEPS panel covering a two-year period (Cohen 

J., 1997). As a result of the overlapping panel design, MEPS annual data for 1997 and 

beyond are constructed based on data collected from two consecutive panels. 

MEPS Expenditures Defined 

Total medical expenditures in MEPS are defined as the sum of direct payments for care

provided during the year, including out-of-pocket payments and payments by third-party

payers (e.g., private insurance, Medicare, Medicaid, and other sources), rather than the 

amount billed by the provider for the care provided (i.e., charges). Payments for hospital 

and physician services, ambulatory physician and nonphysician services, prescribed 

medicines, home health services, dental services, and various other medical equipment 

and services that were purchased or rented during the year are included. Payments for

over-the-counter drugs and phone contacts with providers are not collected in MEPS. 

Provider charges for health care are not considered a proxy for payments, primarily due 

to two important trends that have occurred since the mid 1990s (Zuvekas and Cohen, 

2002). First, pressure to contain health care costs by employers has increased insurers’ 

leverage to negotiate substantial discounts with providers. Second, the insurance 

industry made significant movement toward capitation as a way of increasing the 

incentive for providers to contain costs by being subjected to financial risk for high 

levels of utilization. As a result, for a sizeable number of medical events, charges have

become virtually meaningless as a measure of payments. Nevertheless, charges are 

collected in MEPS because they are highly correlated with payments and are 

incorporated in the imputation process for missing expenditure data wherever possible 

(see Example 3 below). 

MEPS Household Expenditure Data Collection 

Primary data collection in the MEPS-HC employs computer-assisted personal 

interviewing (CAPI). The HC questionnaire is designed to collect use and expenditure 

data for two consecutive years through a series of five interviews. In general, annual 

health care utilization and expenses for sample persons are derived from information 

collected in three of the five interviews (Cohen J., 1997). 

Figure 1 provides a pictorial summary of the data collection process for medical events

and expenses in MEPS. For each person in a sample household, the core instrument 

collects detailed data about medical care received as well as charges and payments for 

each health care event reported in the utilization section. Medical events reported are 

grouped into the following categories: office-based medical provider visits, hospital 

emergency room visits, hospital outpatient visits, hospital inpatient stays, dental visits, 

home health, prescribed medicines, and other medical expenses. Payments for each event

are itemized according to the following 10 source of payment categories: out of pocket, 

Medicare, Medicaid, private insurance, Veteran’s Administration, TRICARE, Other 

2
Federal sources, Other State and local sources, Workers’ Compensation, and Other 

unclassified sources. Payments for a particular medical event can be made across one or 

a combination of sources (though total payments for a small proportion of events each 

year are considered to be $0, which occurs when it is reported that no payments were or 

will be made). Total expenses for a given event are obtained by summing across all 

payment sources. 

Figure 1. Illustration of collection of medical event and source of payment data: MEPS 

 

Nonresponse on payments for a particular medical event may occur for any potential

payment source. However, it is not unusual for respondents to report the amount paid out 

of pocket and that a third-party source(s) paid an unknown amount (i.e., partial item 

nonresponse). 

MEPS Expenditure Estimation Strategy

In addition to the HC, MEPS expenditure data are also collected in the Medical Provider 

Component (MPC) of the survey. The purpose of the MPC is to collect data directly

from a sample of medical providers to reduce the level of missing data and to improve 

the accuracy of expenditure estimates that would be obtained by relying solely on 

household responses (Machlin and Taylor, 2000, and Cohen J. et al., 1997). Data from 

the MPC are considered to be more accurate on average than comparable data reported 

by household respondents in the HC. 

Data obtained in the MPC are linked to medical events reported in the HC based on a 

probabilistic matching procedure (Winglee et al., 1999). As a consequence of the 

matching process, each medical event reported in the HC will have expense data from

both the HC and MPC, one of these sources, or neither source (i.e., complete missing 

payment data). A hierarchical approach is used to develop complete data for 

expenditures as follows: 1) start with household reported medical events, 2) use MPC 

expense data where available, 3) use HC expense data if no MPC data available, and 4)

impute any missing information. Table 1 shows the distribution by source of expenditure 

3
data (i.e., HC, MPC, or imputed) in 2001 for each type of event category, and the 

subsequent discussion provides an overview of the imputation process. 

Table 1. Distribution of source of expenditure data for survey-reported health care events, by

type of service, 2001 MEPS

Hospital events 

Office 

visits

Outpatient 

visits

Emergency 

room visits

Inpatient 

stays 

Dental 

visits1 Homehealth2

Number of events 142, 793 15, 763 5, 904 3, 405 26,438 3,155 

Percent distribution by source of data3

Total 100.0 100.0 100.0 100.0 100.0 100.0

MPC 27.9 46.7 47.9 61.4 -- 42.3

HC 17.5 6.2 8.1 3.7 47.1 9.4 

Imputed: Partial

4 19.2 8.2 9.7 4.9 11.8 0.1 

Imputed: Full 35.3 38.9 34.3 30.0 41.1 48.2

1

Dental care providers are not surveyed in the MEPS Medical Provider Component, so MPC category is not

applicable. 2

Expense data for home health are collected on a monthly rather than a per visit basis. 3

Percentages for office visits do not add to exactly 100.0 due to rounding. 4

Includes events where expense information was imputed for some but not all payment sources. 

 

Imputation Process 

Separate imputations are conducted for each event type category because relevant

variables and statistically significant correlates of expenditures vary by type of event.

However, insurance coverage is utilized for all imputations regardless of event type 

because generosity of payments is associated with type of coverage. For example, 

Medicaid payments are typically less generous than private insurance payments for 

comparable services. 

Missing expenditure data for health care events reported in the survey are completed 

through a weighted hot-deck imputation procedure (Cox, 1980), with data from the MPC 

used as the primary donor source wherever possible. In general, the hot-deck procedure 

sorts donor events (complete data) and recipient events (missing data) into imputation

cells based on important predictors of expenses available in MEPS. For example, the 

imputation procedure for hospital inpatient events sorts donors and recipients into cells 

based on insurance coverage of the sample person, number of nights in the hospital, 

reason for hospitalization, whether the hospital admission immediately followed an 

emergency room visit, as well as region and urbanization level of the person’s residence. 

Whenever possible, a donor is selected within the same cell as a recipient to complete a

recipient record. However, if there are fewer donors than recipients in a cell, cells are 

collapsed in a predetermined order until a 1:1 ratio of donors to recipients is achieved. In 

general, the order used for cell collapsing is determined based on the relative strength of 

the associations between the classification variables and expenses. 

Imputations are handled somewhat differently depending on 1) whether all or some 

potential sources of payment are missing and 2) whether the total charge for the event 

was reported or not. Following are examples of three different scenarios for imputation

of hospital inpatient expenses. These examples assume that donors and recipients match

on the pertinent correlates of expenditures (e.g., insurance coverage, number of nights in 

the hospital, reason for hospitalization, whether the hospital admission immediately

followed an emergency room visit, region, and urbanization). 

4
Example 1. Complete imputation

Payment source Donor Recipient (pre-imputation) Recipient (post-imputation)

Medicare $1,840 Missing $1,840 

Private insurance $792 Missing $792 

Total expenses $2,632 -- $2,632 

In Example 1, it was reported that a sample person had a hospital inpatient stay and was 

covered by Medicare and private insurance but the respondent did not know the amount 

paid by either source for that stay. The donor record that was selected for this recipient 

in the hot-deck procedure was an inpatient stay where the hospital was paid a total of 

$2,632, of which $1,840 was from Medicare and $792 was from a supplemental private 

insurance policy. These identical values were imputed to the recipient record. 

Example 2. Partial imputation

Payment source Donor Recipient (pre-imputation) Recipient (post-imputation)

Out of pocket $26 $5 $5 

Private insurance $971 Missing $992 

Total expenses $997 -- $997 

In Example 2, it was reported that a sample person had an inpatient hospitalization, was 

covered by private insurance, and that $5 was paid out of pocket but the respondent did

not know the amount paid to the hospital by private insurance. The donor record that 

was selected for this recipient in the hot-deck procedure was an inpatient stay where the 

hospital was paid a total of $997, of which $26 was paid out of pocket and $971 was 

from private insurance. In this situation, the total amount paid for the event from the 

donor ($997) was imputed to the recipient record, the reported out-of-pocket amount 

($5) was retained, and the difference ($992) was imputed to the recipient record as a 

private insurance payment. 

 Example 3. Imputation using total charge

Payment source Donor Recipient (pre-imputation) Recipient (post-imputation)

Total charges $5,171 $4,173 $4,173 

Total expenses $4,248 missing $3,421 

Medicare $3,411 missing $2,737 

Private insurance $837 missing $684 

As described earlier (see section on MEPS Expenditures Defined), charges are not 

identical to but are highly correlated with expenditures (payments) made for health care. 

In most instances, when there are missing data on payments for a health event reported 

in the survey there are also missing data on charges. However, in situations where the 

respondent reports the total charge for an event but does not know the actual payments, 

the reported information on charges is used to improve the accuracy of the imputation. 

To illustrate the use of total charge information when available, in Example 3 the 

respondent reported there was $4,173 in hospital facility charges for the reported

inpatient stay. The donor record selected for the imputation in the hot-deck procedure 

showed $5,171 in total charges and $4,248 in total expenses. The first step imputes total 

expenses to the recipient record by applying the ratio of total expenses to total charges 

5
on the donor record (4,248/5,171) to the total charges on the recipient record ($4,173). 

Then, the imputed total expense on the recipient record ($3,421) is allocated across the

two potential sources of payment, Medicare and private insurance, in the same 

proportion as on the donor record (i.e., 837/4,248 and 3411/4,248 for Medicare and 

private insurance, respectively). 

Summary 

MEPS is an ongoing survey that collects data on the utilization and expenditures for 

health care in the U.S. civilian noninstitutionalized population. Given the complexity of 

the U.S. health care system and the wide range of public and private financing 

arrangements, it is difficult to collect complete information on health care expenses. 

To maximize the completeness and accuracy of expenditure data, MEPS integrates data

on utilization and expenditures from the Household Component of the survey with data 

from a sample of providers that participate in the Medical Provider Component of the 

survey. To complete medical expenditure data that were not obtained from either 

component, a weighted hot-deck imputation procedure is used. The primary advantage of

this procedure is that the distribution of data values (including the imputed ones) will

look similar to the distribution of the values in the population (Korn and Graubard, 

1999). 

The hot-deck procedures used to complete missing expenditure data in MEPS are based

on statistical as well as substantive considerations regarding the U.S. health care

financing system. For example, type of health insurance coverage is used as an auxiliary

variable in the imputations for all health service type categories because of differences in 

average payments between insured and uninsured persons as well as varying generosity

of payments by type of insurance coverage. In contrast, length of stay is incorporated as

a classification variable in the hot deck only for inpatient stays because it is significantly

associated with expenditures for hospital inpatient stays, but is irrelevant when imputing 

expenses for other types of health care events. 

In summary, the dual objectives of imputing missing expenditure data in MEPS are to 

maximize sample sizes available for analysis and to reduce the risk of nonresponse bias 

associated with exclusion of cases with missing data. However, the imputation approach 

used is inherently complex, resource intensive, and leads to underestimation of variances

for survey estimates without an additional correction. While it is difficult to assess the 

impact of imputation on variances, the Center for Financing, Access, and Cost Trends at 

AHRQ is currently conducting methodological research to estimate the magnitude of the 

impact. Results of a preliminary investigation of the impact of the expenditure 

imputations in MEPS have been reported (Baskin, 2004). 

References

Baskin, R., Wun, L., Sommers, J., et al. Investigation of the impact of imputation on 

variance estimation in the Medical Expenditure Panel Survey. American Statistical 

Association 2004 Proceedings. 2004. 

 

6
Cohen, J. Design and Methods of the Medical Expenditure Panel Survey Household 

Component. MEPS Methodology Report No. 1. AHCPR Pub. No. 97-0026. Rockville, 

Md.: Agency for Health Care Policy and Research, 1997. 

Cohen, J., Monheit, A., Cohen, S., et al. The Medical Expenditure Panel Survey: A 

National Health Information Resource. Inquiry, 33: 373-389 (Winter 1996/97). 

Cohen, S. Sample Design of the 1996 Medical Expenditure Panel Survey Household 

Component. MEPS Methodology Report No. 2. AHCPR Pub. No. 97-0027. Rockville, 

Md.: Agency for Health Care Policy and Research, 1997. 

Cox, B. The weighted sequential hot deck imputation procedure. American Statistical 

Association 1980 Proceedings of the Section on Survey Research Methods, 721-726. 

1980. 

Korn, E. and Graubard, B. Analysis of Health Surveys. Wiley Series in Probability and 

Statistics. 1999. 

Machlin, S. and Taylor, A. Design, Methods, and Field Results of the 1996 Medical 

Expenditure Panel Survey Medical Provider Component. MEPS Methodology Report 

No.9. AHRQ Pub. No.00-0028. Rockville, Md.: Agency for Healthcare Research and 

Quality, 2000. 

National Center for Health Statistics. Health, United States, 2002 (361-362). Hyattsville, 

Md.: 2002. 

Winglee, M., Valliant, R., Brick, M., and Machlin, S. Probability matching of medical 

events. Journal of Economic and Social Measurement 23 (1999) 1-12. 

Zuvekas, S. H. and Cohen, J. W. A guide to comparing health care expenditures in the 

1996 MEPS to the 1987 NMES. Inquiry, Spring 2002; 39:76-86. 

Acknowledgments

The authors wish to thank Trena Ezzati-Rice, Joel Cohen, and Steven Cohen for their 

helpful reviews of the paper. 

7