The amount and level of methodological detail published in MCC research papers varies greatly. Lack of consistency and detail regarding inclusion and aggregation of diagnosis codes hinders our ability to interpret research results and judge methodological quality. For example, in a manuscript describing chronic disease clustering, Schafer and colleagues provide a list of the specific ICD-10 codes they investigated in their study (Schafer et al., 2010). Conversely, in a paper looking at prevalence of chronic conditions in the VA Health Care System, Yu and colleagues did not report the ICD-9 codes that were examined. Instead the authors stated that “the diagnoses and specific codes used to identify each condition are available upon request from the authors” (Yu et al., 2003). For the purpose of developing this paper, we contracted Yu and his colleagues to obtain the list of the diagnoses and ICD-9 codes used in their study. Unfortunately, we were unable to reach the lead author and could not obtain the information.2 However, an inquiry regarding a different, but related investigation (Yoon et al., 2011) resulted in a list of diagnoses and ICD-9 codes (in SAS) that could be examined and compared to other studies.
A lack of consistency and detail in reporting diagnosis codes is only one example of the variability in methods sections in published MCC studies. Variability is also a concern in understanding why specific conditions are examined vs. others, why certain diagnosis codes are excluded from analyses, how chronic condition categories are constructed, how costs are allocated to chronic condition categories after dropping certain diagnosis codes, etc. A repository of author’s ICD-9 codes is a potential mechanism by which authors could explain why certain diagnosis codes were included or excluded from specific analyses. However, to effectively address the variability across MCC studies a reporting framework or set of criteria, such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), may be necessary to begin to standardize efforts and reporting across researchers (Moher et al., 2009).
2 Personal communication with available authors of Prevalence and Costs of Chronic Conditions in the VA Health Care System in Medicare Care Research and Review, 2003.