Assessing the effects of multimorbidity (MM), the co-occurrence of several conditions, is contingent on the way it is measured [10, 11]. Current definitions usually apply an additive approach, summing chronic diseases out of predetermined lists [11]. A wide range of variation within single chronic conditions can be explained by diversity in the co-occurrence of related conditions, sequel of the condition of interest (e.g., complications), the stage of the disease, and presence of other “non-related” conditions [12, 13]. To effectively reflect the burden of morbidity, beyond a simple count or “list” of the common chronic conditions that are present in individuals or populations, valid methodologies that take into account combinations and interactions between conditions are available [14]. These classification systems categorize patients’ morbidity according to all diagnoses registered at medical encounters during a defined period of time (usually a year). Relying on clinical and epidemiological considerations, diagnoses are classified into morbidity groups, spanning from minor acute to major chronic illnesses, with various degrees of severity. Previous studies have shown that encompassing morbidity as part of a complex morbidity measurement system is highly reliable and valid, in various countries and population groups [15]. Nonetheless, even the existing comprehensive measures of morbidity fail to capture the full complexity of states that are related to a persons’ health, as they are based only on clinical diagnoses. An emerging construct is that of patient complexity which acknowledges that morbidity burden is influenced not only by health-related characteristics, but also by socioeconomic, cultural, environmental, and behavioral attributes [10]. A broader definition of MM is needed also because diseases are more likely to occur and to be more severe in socially disadvantaged populations [16, 17]. Inequity in health, defined as “differences in health which are not only unnecessary and avoidable but, in addition, are considered unfair and unjust” [18], is at the focus of societies and health systems worldwide. Despite impressive improvements in the health status of populations, there is increasing evidence of widening health gaps that span the socioeconomic spectrum and range of minority ethnic groups [19, 20, 21].