Most MCC research in the United States has primarily been conducted on chronic conditions that are highly prevalent and well-known. Low-prevalence conditions and less prevalent combinations of conditions have not been well studied, even though patients with these findings represent one-third of all Medicare beneficiaries and 79% of expenditures. Within the “long tail” of the distribution, the sheer number of combinations, and the small cell size within each of those combinations of chronic disease (10–11 beneficiaries nationally, on average), present a great methodological challenge for the study of patients with similar combinations of diagnoses.
White paper #1 reviews the findings in the literature with regards to disease combination complexity, and discusses how variables in study methodologies can greatly influence results. Critical design decisions include sources of data, number of disease codes to be included in the analysis, and the degree to which these primary codes are grouped into a limited set of high-level disease entities. Significant variation in these methodologies hampers interpretation across studies.
As discussed in white paper #2, the literature reports that MCC prevalence is strongly correlated with older age, greater cost, poorer quality of life, greater health care utilization, and higher mortality. Women, African-Americans, and non-Hispanic Whites have the highest MCC prevalence. Hispanics and Asian-Americans have lower prevalence, but Asians/Pacific Islanders had the highest mortality and cost per case compared to all other groups.
Several available datasets and grouping systems were reviewed that can be used to further research MCC and MCC practice.