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Many cost-of-illness studies do not include all costs of a particular injury or illness, and may be misleading

Policymakers and health care providers look to cost-of-illness (COI) studies to identify the cost of specific illnesses and injuries. These results help drive decisions about future insurance benefits, research efforts to curb and control disease and injury, and development of programs to improve health. Yet COI studies have significant limitations, according to a new study.

The researchers conducted a systematic review of COI studies published from 2000 to 2004. A detailed review of the COI literature identified 52 studies that met inclusion criteria (that included studies containing more than one component of care and studies that were original research). These 52 studies used different approaches to assessing care costs and were often unclear about how they calculated the cost of illness. Also, many studies did not include all aspects of care in their cost assessments, thus underestimating the full cost of treating the disease or injury under study. Across this systematic review, articles contained only an average four components of care.

Studies also varied in the cost perspectives they addressed. For example, nearly half of the studies captured direct costs from the perspective of society, and a third captured the perspective of either the employer or insurance-based health care. The most frequently analyzed components of care, in order of frequency, were outpatient care, hospitalization, prescription medication, emergency department, other noncategorized care components, nursing home, home care, and laboratory or test procedures.

The findings were based on employer-based health insurance and claims data (21 of 52 studies), NCHS sources (11 studies), as well as Medicare and Medicaid data (6 articles). The study was supported by the Agency for Healthcare Research and Quality (HS15009).

More details are in "Cost-of-illness studies in the United States: A systematic review of methodologies used for direct cost," by Gerd Clabaugh, M.P.A., and Marcia M. Ward, Ph.D., in the January-February 2008 Value In Health 11(1), pp. 13-21.

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