Table 1

Description of the included studies

Author(s), countryMethodological approachStudy periodDefinition high-costStudy population: inclusion and exclusion criteriaCost data
Aldridge and Kelly,57 USADescriptive2011Top-5%US populationTotal spending was identified from a combination of data from Medical Expenditure Panel Survey, the Health and Retirement Study, peer-reviewed literature, published reports, 2011 MEPS and 2011 National Health Expenditure Accounts.
Ash et al,58 USADescriptive, logistic regression1997–1998Top-0.5% with highest predicted costs, top-0.5% prior cost.Individuals eligible for at least 1 month in each of the two study years.MEDSTAT MarketScan Research Database, consisting of inpatient and outpatient care from individuals covered by employee-sponsored plans. Outpatient pharmacy costs were excluded.
Bayliss et al,59 USAPredictive modelling, cluster analysis2014Top-25%Members with new Kaiser Permanente Colorado benefits and who completed the Brief Health Questionnaire.Per-member per-month costs from Kaiser Permanente Colorado health system.
Beaulieu et al,28 USADescriptive, logistic regression2011–2012Top-10%Fee-For-Service Medicare population. Excluding patients <65 years, enrolled in Medicare advantage and those not continuously enrolled in parts A and B.Standardised Medicare costs, excluding prescription drug charges.
Boscardin et al,60 USADescriptive, logistic regression2009Top-10%Employees enrolled in the Safeway health insurance programme in 2009, with biometric and self-reported health status data (Health Risk Questionnaire).
Excluding dependents covered through a family member.
Safeway’s health plan.
Buck et al,61 USADescriptive1995Top-10%Medicaid population in 10 states.
Excluding dually eligible, ≥65 years, enrolled in capitated plans, missing sex or birthdate.
Total Medicaid expenditures.
Bynum et al,16 USADescriptive, multinominal logistic regression2010–2011Top-10% in each state
Persistently HC, died in 2011, or converted
Dually eligible adults with full Medicaid eligibility; in the 36 states that had usable and complete Medicaid data.Medicare and Medicaid.
Chang et al,62 USADescriptive, logistic regression2007–2009Consistent high-user: top-20% in four consecutive half year periods (≡ 6.14% of the population)
Point high-user: top-6.14% in 1 year
Enrollees from four health plans who were (1) continuously enrolled, (2) incurred ≥$100 each year, (3) from the 4 largest plans; (4) aged between 18 and 62 years in 2007.
Excluding those who died.
Commercial health plans.
Charlson et al,63 USAQuantile regression2007 (6 months)Top-5%, top-10%All enrollees of the MMC Plan who had an assigned primary care provider at Lincoln Medical and Mental Health Center.Metroplus Medicaid Managed Care costs, including inpatient, outpatient, emergency room, laboratory tests and prescription drugs.
Charlson et al,64 USAQuantile regression2009–2010Top-5%, top-10%Union of health and hospital workers in the Northeast, those who were consistently eligible for benefits over at least 22 months in 2009 and 2010 (self-insured trust fund), who also received DCG codes.Inpatient, outpatient, emergency room, laboratory tests, behavioural health and prescription drugs.
Chechulin et al,22 CanadaLogistic regression2007/2008–2010/2011Top-5%All Ontario residents serviced by the Ontario healthcare system during the fiscal year 2009/2010. Patients under 5 years or who died during this year were excluded.Total health system costs (including Long Term Care), excluding outpatient oncology, outpatient dialysis, and outpatient clinic.
Cohen et al,65 USALogistic regression1996–2002Top-10%,Nationally representative sample of the Medical Expenditure Panel Survey.All direct payments to providers by individuals, private insurance, Medicare, Medicaid and other payment sources for: inpatient and outpatient care, emergency room services, office-based medical provider services, home healthcare, prescription medicines and other medical services and equipment.
Coughlin et al,66 USADescriptive2006–2007
(1 year)
Top-10%Medicare beneficiaries and dual eligibles.Spending paid for by the public programmes.
Coughlin and Long,67 USADescriptive2002–2004Various. Top-1%,
Top-5%, Top-10%,
Top-25%, Top-50%
2002 national Medicaid population (living in institutions and community).
Excluding who received only State Children’s Health Insurance Program (SCHIP) coverage or never full benefits. Top-0.1% of spenders.
Crawford et al,68 USANeural network modelling1999–2001Top-15%Members of a health plan, where American Healthways, Inc. provided disease management services. Only members with 24 months continuous enrolment were included.Health plan costs.
DeLia,20 USADescriptive, multinomial regression2011–2014Top-1%, top-2%–10%,
Persistently extreme: 4 years top-1%
Persistently high: 4 years in top-10%
Medicaid/Children’s Health Insurance Program (CHIP) beneficiaries in New Jersey, newly covered individuals under the Affordable Care Act (ACA) (2014) were excluded; Medicaid/Medicare dual eligibles were excluded.Medicaid FFS claims and managed care encounters and CHIP.
de Oliveira et al,18 CanadaDescriptive2012Top-10%, top-5%, top-1%. Mental health HC patients: mental health>50% of total costs.All adult patients (18 years and older) who had at least one encounter with the Ontario healthcare system in 2012.
Excluding all individuals who did not have a valid Ontario Health Insurance Plan number.
Most publicly funded healthcare services.
Figueroa et al,30 USADescriptive, χ2 2012Top-10%Adults 18–64 year without FFS Medicare coverage or Medicare Advantage coverage.Massachusetts All-Payer Claims database; nearly a universal account of all healthcare delivered in the state with the exception of Medicare FFS.
Figueroa et al,39 USADescriptive2012Top-10%All Medicare patients, excluding those with Medicare Advantage coverage, who were not continually enrolled in parts A and B.Standardised Medicare costs.
Fitzpatrick et al,21 CanadaDescriptive, logistic regression2003/2005 and 5-year follow-upTop-5%Participants from two cycles of Canadian Community Health Survey (CCHS) surveys, representative of the population ≥12 years and living in private dwellings. ≥18 years. Excluding baseline high cost.Ontario health insurance plan.
Fleishmann and Cohen,69 USALogistic regression1996–2003Top-10%, top-5%Nationally representative sample of the Medical Expenditure Panel Survey.All direct payments to providers by individuals, private insurance, Medicare, Medicaid and other payment sources for: inpatient and outpatient care, emergency room services, office-based medical provider services, home healthcare, prescription medicines and other medical services and equipment.
Ganguli et al,23 USADescriptive, retrospective chart review, interview analysis2005–2011Five archetypal patients among the 50 costliest/1500 highest cost patientsPatients selected by costs and a prospective risk score to participate in a Centers for Medicare and Medicaid care management project, >18 years and had sufficient cognitive capacity to participate in an interview, or if deceased had family members who were able to give sufficient information.Total Medicare payments.
Graven et al,29 USADescriptive2011–2013Top-10%,
Episodically high-cost, persistently high-cost
Adults ages 19 and over, enrolled in Oregon Medicaid, commercial or Medicare Advantage programmes. Only those with continuous enrolment in 2011 and 2012 were included. Excluding dual eligibles and individuals who had ‘coordination of benefit’- laims or with negative total spending in any of the quarters.Total Medicaid, commercial or Medicare Advantage payments (acute care expenditures), excluding spending on prescription drugs.
Guilcher et al,19 CanadaDescriptive1 April 2010–31 March 2011Top-5%All persons eligible for provincial health insurance residing in the community, who had at least one interaction with the system in the last 5 years.All publicly funded healthcare in a universal public healthcare system.
Guo et al,36 USADescriptive, logistic regression1999–2000Top-10% of average monthly expensesMedicaid, FFS recipients younger than 65 years.
Excluding nursing home recipients.
Medicaid costs.
Hartmann et al,70 GermanyLogistic regression2010–2011Top-10%Enrollees 18 years and older of AOK Lower Saxony, Germany’s 10th largest statutory health insurer.Inpatient and outpatient care, sickness benefits, rehabilitation, home nursing, ambulatory drug supply, prescribed therapeutic appliances and remedies.
Hensel et al,71 CanadaDescriptive, logistic regression1 April 2011–31 March 2012Top-1%, top-2%–5%, top-6%–50%, bottom-50%, and zero-cost referent groupAll Ontario residents, with a valid Ontario healthcare, 18 years of age or older and medical care costs greater than zero.Ontario health insurance plan, for all hospital and home care services, including physician care, costs related to outpatient physician services were not included
Hirth et al,72 USADescriptive, logistic regression2003–2008High: top-10%
Moderate: top-10%–30%
Low: bottom-70%
Usually low
Sometimes high
Often high
Usually high
Under-65 population (Truven Health MarketScan database); enrollees and dependents of more than 100, mainly self-insured, medium and large employers.
Only people enrolled continuously are included.
Attrition (a minority was enrolled each year) due to several reasons: death, retirement, children ageing out of dependent status and so on.
Data from all carve-outs (eg, prescription drug and mental health), including claims for which the deductible is imposed. All spending was adjusted to 2008 dollars using the medical cost Consumer Price Index.
Excluding out-of-plan spending (eg, OTC drugs and travel costs).
Hunter et al,73 USADescriptive, linear regressionFiscal year 2010Top-5%Cohort from Veterans Affairs (VA) administrative records, who were eligible for and received care in study period. Excluding individuals with schizophrenia, bipolar depression, other psychosis, alcohol dependence and abuse, drug dependence and abuse, post-traumatic stress disorder and/or depression.Inpatient, outpatient, pharmacy and non-VA contract care.
Hwang et al,37 USADescriptive, logistic regression2008–2011Top-10%Employees from a large employer in Pennsylvania and the employees’ dependents. Only those continuously enrolled.Amount paid by the insurer and the amount of cost sharing paid by individuals.
Izad Shenas et al,74 USAData mining techniques/predictive modelling2006–2008Top-5%, top-10%, top-20%Nationally representative sample of the Medical Expenditure Panel Survey, household individuals ≥17 years (redundant records, or with zero personal-level weights were removed).All direct payments to providers by individuals, private insurance, Medicare, Medicaid and other payment sources for: inpatient and outpatient care, emergency room services, office-based medical provider services, home healthcare, prescription medicines and other medical services and equipment.
Joynt et al,75 USADescriptive2011 and 2012Top-10%All Medicare patients, excluding those with Medicare Advantage coverage, who were not continually enrolled in parts A and B, or who died during the study period.Standardised Medicare costs.
Joynt et al,26 USADescriptive, linear regression2009–2010Top-10%Medicare >65 years population.
Excluding decedents, any Medicare advantage enrolment, not continuously enrolled.
Inpatient and outpatient services.
Krause et al,76 USALogistic regression2009–2011Top-5%, top-1%, >$1 00 000Enrollees of Blue Cross Blue Shield of Texas, only members 18–63 years, with a zip code in Texas and continuous enrolment in 2009 were included.Total claims expense, including expenditures for hospital care, outpatient facility services and professional services.
Ku et al,34 TaiwanDescriptive, generalised estimating equations2005–2009Top-10%, top-11%–25%Survey respondents 65 years of age and older.National health insurance.
Lauffenburger et al,77 USADescriptive, group-based trajectory modelling2009–2011Top-5%Patients ≥18 years, with continuous eligibility for the entire calendar year, with ≥1 calendar year before their entry year and with ≥1 medical and pharmacy claim in both the baseline and entry year.Medical and prescription data of Aetna, a large US nationwide insurer.
Lee et al,78 USADescriptive, cluster analysis2012Top-10%Medicare patients hospitalised exclusively at Cleveland Clinic Health System and received at least 90% of their primary care services at a CCHS facility.CCHS facility costs, postacute care services were only included for those patients who were admitted to a CCHS postacute care facility.
Leininger et al,79 USADescriptive, logistic regression2009–2010 (1 year)Top-10%New enrollees for Medicaid who completed a self-reported health needs assessment.Medicaid costs.
Lieberman et al,33 USADescriptive1995–1999Top-5%Medicare FFS beneficiaries.Medicare spending.
Meenan et al,80 USARisk modelling.1995–1996Top-0.5%, top-1%Enrollees of six Health Maintenance Organizations (HMOs), eligible for some period in 1995 and 1996 and who had an outpatient pharmacy benefit. Medicare Cost enrollees were excluded.Total claims, including inpatient, outpatient, radiology, pharmacy, durable medical equipment, long-term care, laboratory.
Monheit,31 USADescriptive, logistic regression1996–1997Various. Top-1%,
Top-2%, Top-5%,
Top-10%, Top-20%, Top-30%, Top-50%.
Representation of non-institutionalised civilian US population (survey respondents).Total payments (including Out-Of-Pocket, uncovered services and third-party payments).
Powers and Chaguturu,9 USADescriptive2014Top-1%Patients of Partners HealthCare integrated delivery system.Medicare, Medicaid, commercial insured populations are compared.
Pritchard et al,35 USADescriptive2011Top-5%Managed care population, of all ages, with at least 180 days continuous enrolment prior 1 January 2011, patients with gaps in enrolment greater than 30 days were excluded (so no uninsured or patients enrolled in traditional FFS Medicare or Medicaid programmes).Medical and pharmaceutical claims for more than 80 US health plans, the total amount reimbursed by the insurer plus the plan member’s out-of-pocket share.
Rais et al,38 CanadaDescriptive2009–2010
(1 year)
Top-5%Cost consuming users of hospital and home care services at the provincial level.Hospital and home care services.
Excluding: primary care and long-term care use.
Reid et al,81 CanadaDescriptive1996–1997
(1 year)
Top-5%≥18 years and older enrolled in the province’s universal healthcare plan.Medical services costs in a universal healthcare plan (physician and hospital services).
Reschovsky et al,27 USADescriptive, logistic regression2006 or 12 months before deathTop-25%Medicare FFS beneficiaries, ≥1 Community Tracking Survey survey, with usual source of care physician.
Excluding end-stage renal disease beneficiaries.
Standardised total costs of Medicare parts A and B.
Riley,82 USADescriptive1975–2004Top-1%
Medicare, beneficiaries entitled to parts A and B.Medicare costs.
Robst,83 USADescriptive, logistic regression2005–2010Top-1% in some years, or in 6 yearsMedicaid beneficiaries with fee-for-service coverage for at least 6 months in all 6 years.Medicaid.
Rosella et al,24 CanadaDescriptive, multinomial logistic regression2003–2008Top-5%
Top-1%, top-2%–5%, top-6%–50%
Ontario residents.
Participants of the CCH Survey.
Excluding: institutionalised. Full-time members of the Canadian forces. Persons living in remote areas/aboriginal reserves. Ages 12–18 years.
Those covered by Ontario’s Universal Health Insurance Plan.
Excluding some prescription drug costs, allied health services, dental care, eye care and assistive devices.
Snider et al,25 USALogistic regression2004–2009Top-20%Employees from large US employers, from the Thomson Reuters Marketscan Commercial Claims and Encounters database with both body mass index and claims in any given year. Pregnant women and underweight employees were excluded.All inpatient, outpatient and prescription claims.
Tamang et al,32 DenmarkDescriptive, prediction modelling2004–2011Top-10%Entire population of Western Denmark, with a full year of active residency in year 1.Danish National Health Service.
Wammes et al,17 the NetherlandsDescriptive2013Top-1%, top-2%–5%, bottom-95%Beneficiaries of one Dutch health insurer.Dutch curative health system, basic benefit package including voluntary complementary insurance benefits.
Wodchis et al,15 CanadaDescriptive1 April 2009–31 March 2012Top-1%
People with a recorded age of less than 105 years who were alive on 1 April in any of the three study years and who had a valid Ontario healthcare at any time between 1 April 2009 and 3 March 2012.Costs refer to healthcare expenditures that have been allocated to patient encounters for healthcare.
All medically necessary care, both acute and long term, as covered by public health insurance.
Excluding public health, community service agencies and many other programmes, as well as for administrative (government) staff. Private home care, privately insured medication costs.
Zhao et al,84 USADescriptive, linear regression1997–1999Top-0.5%Private insured, whose claims were covered in the Medstat MarketScan Research Database; a multisource private sector healthcare database. All cases with a pharmacy benefit and at least 1 month of eligibility in each of the first two study years, or the last two study years.Total medical costs, including inpatient plus ambulatory plus pharmacy costs, and deductibles, coinsurance and coordination-of-benefit payments.
Zulman et al,85 USADescriptive, regression analysesFiscal year 2010Top-5%Veterans served by the VA System, who received inpatient or outpatient VA care.Outpatient and inpatient, pharmacy, VA-sponsored contract care.