Development and Application of a Population-Oriented Measure of Ambulatory Care Case-Mix
Abstract
This article describes a new case-mix methodology applicable primarily to the ambulatory care sector. The Ambulatory Care Group (ACG) system provides a conceptually simple, statistically valid, and clinically relevant measure useful in predicting the utilization of ambulatory health services within a particular population group. ACGs are based on a person's demographic characteristics and their pattern of disease over an extended period of time, such as a year. Specifically, the ACG system is driven by a person's age, sex, and ICD-9-CM diagnoses assigned during patient-provider encounters; it does not require any special data beyond those collected routinely by insurance claims systems or encounter forms. The categorization scheme does not depend on the presence of specific diagnoses that may change over time; rather it is based on broad clusters of diagnoses and conditions. The presence or absence of each disease cluster, along with age and sex, are used to classify a person into one of 51 ACG categories. The ACG system has been developed and tested using computerized encounter and claims data from more than 160,000 continuous enrollees at four large HMOs and a state's Medicaid program. The ACG system can explain more than 50% of the variance in ambulatory resource use if used retrospectively and more than 20% if applied prospectively. This compares with 6% when age and sex alone are used. In addition to describing ACG development and validation, this article also explores some potential applications of the system for provider payment, quality assurance, utilization review, and health services research, particularly as it relates to capitated settings.
Integrity signals
Registry
Cites
Statistics
Claims the paper makes
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The comorbidity index was calculated via the Johns Hopkins Aggregated Diagnosis Groups (ADG) algorithm, a well validated case mix metric for ambulatory populations.
“The comorbidity index was calculated via the Johns Hopkins Aggregated Diagnosis Groups (ADG) algorithm, a well validated case mix metric for ambulatory populations [31].”
From Effects of workload, work complexity, and repeated alerts on alert fatigue in a clinical decision support system (2017) · cites this paper as [31]
Cites
Case mix definition by diagnosis-related groups.
Fetter, R. B., Shin, Y., Freeman, J. L., Averill, R. F., & Thompson, J. D. (1980) · PubMed · Cited by 862 · see citing works
Ambulatory care groups: a categorization of diagnoses for research and management.
Starfield, B. H., Weiner, J. P., Mumford, L. M., & Steinwachs, D. M. (1991) · Europe PMC (PubMed Central) · Cited by 520 · see citing works
Self-citationAdjusting capitation rates using objective health measures and prior utilization.
Newhouse, J. P., Manning, W. G., Keeler, E. B., & Sloss, E. M. (1989) · PubMed Central · Cited by 243 · see citing works
Adjusting Medicare capitation payments using prior hospitalization data.
Ash, A. S., Porell, F. W., Gruenberg, L. W., et al. (1989) · PubMed · Cited by 189 · see citing works
Morbidity in Childhood — A Longitudinal View
Starfield, B. H., Katz, H., Gabriel, A., Livingston, G., Benson, P., Hankin, J. R., Horn, S., & Steinwachs, D. M. (1984) · New England Journal of Medicine · doi:10.1056/nejm198403293101305 · Cited by 118 · see citing works
Self-citationUtilization and Morbidity: Random or Tandem?
Starfield, B. H., Hankin, J. R., Steinwachs, D. M., Horn, S., Benson, P., Katz, H., & Gabriel, A. (1985) · PEDIATRICS · doi:10.1542/peds.75.2.241 · Cited by 81 · see citing works
Self-citationSelection bias in health maintenance organizations: analysis of recent evidence.
Hellinger, F. J. (1987) · PubMed · Cited by 61 · see citing works
Increasing Medicare enrollment in HMOs: the need for capitation rates adjusted for health status.
Thomas, J. W., Lichtenstein, R. L., Wyszewianski, L., et al. (1983) · PubMed · Cited by 38 · see citing works
Tenan, P. M., Fillmore, H. H., Caress, B., et al. (1988) · Journal of Ambulatory Care Management · doi:10.1097/00004479-198808000-00005 · Cited by 33 · see citing works
Horn, S. D., Buckle, J. M., & Carver, C. M. (1988) · Journal of Ambulatory Care Management · doi:10.1097/00004479-198811000-00009 · Cited by 26 · see citing works
Schneider, K. C., Lichtenstein, J. L., Freeman, J. L., et al. (1988) · Journal of Ambulatory Care Management · doi:10.1097/00004479-198808000-00002 · Cited by 23 · see citing works
Paying for HMO Care: Issues and Options in Setting Capitation Rates
Anderson, G. F., Steinberg, E. P., Holloway, J., et al. (1986) · Milbank Quarterly · doi:10.2307/3349925 · Cited by 18 · see citing works
Common sense on extending DRG concepts to pay for ambulatory care.
Gold, M. (1988) · PubMed · Cited by 11 · see citing works
Wasson, J. H., Sauvigne, A. E., Balestra, D. J., et al. (1987) · Medical Care · doi:10.1097/00005650-198710000-00008 · Cited by 5 · see citing works
Adjusting Employer Group Capitation Premiums by Community Rating by Class Factors
Cave, D. G., Schweitzer, S. O., & Lachenbruch, P. A. (1989) · Medical Care · doi:10.1097/00005650-198909000-00004 · Cited by 4 · see citing works
Flagged first, then by citations
Cited by
Sorted by citations
with the HITEC Investigators, Ancker, J. S., Edwards, A., Nosal, S., Hauser, D., Mauer, E., & Kaushal, R. (2017) · BMC Medical Informatics and Decision Making · doi:10.1186/s12911-017-0430-8 · Cited by 709 · see citing works
“The comorbidity index was calculated via the Johns Hopkins Aggregated Diagnosis Groups (ADG) algorithm, a well validated case mix metric for ambulatory populations [31].”
MethodMedical and Psychosocial Diagnoses in Women With a History of Intimate Partner Violence
Bonomi, A. E. (2009) · Archives of Internal Medicine · doi:10.1001/archinternmed.2009.292 · Cited by 364 · see citing works
Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality: A Cohort Study
Padwal, R., Leslie, W. D., Lix, L. M., & Majumdar, S. R. (2016) · Annals of Internal Medicine · doi:10.7326/m15-1181 · Cited by 235 · see citing works
The impact of diabetes on survival following breast cancer
Lipscombe, L. L., Goodwin, P. J., Zinman, B., McLaughlin, J. R., & Hux, J. E. (2008) · Breast Cancer Research and Treatment · doi:10.1007/s10549-007-9654-0 · Cited by 176 · see citing works
Does Continuity of Care Matter in a Universally Insured Population?
Menec, V. H., Sirski, M., & Attawar, D. (2005) · Health Services Research · doi:10.1111/j.1475-6773.2005.0p364.x · Cited by 110 · see citing works
Conrad, D., Fishman, P., Grembowski, D., Ralston, J., Reid, R., Martin, D., Larson, E., & Anderson, M. (2008) · Health Services Research · doi:10.1111/j.1475-6773.2008.00880.x · Cited by 16 · see citing works
- Authors
- Weiner, J. P., Starfield, B. H., Steinwachs, D. M., & Mumford, L. M.
- Affiliations
- Johns Hopkins University (US)
- ORCID
- Weiner, Jonathan P.
- Venue
- Medical Care
- Published
- 1991-05
- Volume
- 29
- Issue
- 5
- Pages
- 452-472
- ISSN
- 0025-7079 (ISSN-L)
- OpenAlex
- W2055675683
- Cited by
- 677
- References
- 15
- Citations by year
- 2026: 3 · 2025: 5 · 2024: 9 · 2023: 9 · 2022: 13 · 2021: 13 · 2020: 19 · 2019: 14 · 2018: 21 · 2017: 23 · 2016: 24 · 2015: 26 · 2014: 28 · 2013: 41 · 2012: 34
- FWCI
- 4.81
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Medical Care (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Agency for Healthcare Research and Quality (HS05505)
- Topics
- Health Sciences › Medicine › Epidemiology › Chronic Disease Management Strategies
- Social Sciences › Economics, Econometrics and Finance › Economics and Econometrics › Healthcare Policy and Management
- Health Sciences › Health Professions › General Health Professions › Primary Care and Health Outcomes
- Keywords
- case-mix classification, ambulatory care utilization, disease clusters, health maintenance organizations, Medicaid, provider payment, capitation, quality assurance, utilization review
- MeSH terms
- Adolescent, Adult, Aged, Ambulatory Care, Child, Child, Preschool, Decision Trees, Demography, Diagnosis-Related Groups, Female, Humans, Infant, Male, Maryland, Middle Aged, Morbidity, Rate Setting and Review, Utilization Review, Models, Statistical, Multivariate Analysis, Cluster Analysis
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review
