The purpose of this paper is to review the published literature that has addressed the associations between disparities and adherence to analgesia among cancer patients. Evidence was examined for outcomes studied, data collection methods, variables studied in relation to adherence, and the magnitude of association based on race and adherence.
We performed a systematic search of studies published between 1990 and the present in Scopus, CINAHL, PubMed, Ovid, PsychInfo, and the EMBASE databases. The inclusion criteria consisted of published articles in the aforementioned databases that were (1) set in the United States, (2) primary studies, (3) employed quantitative design, (4) assessed adherence or compliance to analgesics or adequacy of pain management using the Pain Management Index (PMI), (5) sample was exclusively minority or may have had a comparative group. The title and abstract of each article in the the search results was reviewed for relevance to study aims and inclusion and exclusion criteria, and any duplicates were eliminated. A total of 6 studies were found using this method ( Table 1 ), and an additional study was found in the reference list of 1 of these 6.
The 7 included studies were observational in nature; 4 were cross-sectional [4,12,15,16], 2 were retrospective [3,14], and 1 was prospective and used objective measures of analgesic adherence  ( Table 2 ).
Defining and Operationalizing Adherence
Meghani and Bruner  point out that analgesic adherence is a “heterogeneous construct that lends itself to varied results and interpretations depending on the measurements used or dimensions studied.” Adherence to analgesia was explicitly defined in all 7 studies ( Table 3 ). One study reported an adherence rate that was the total dose over 24 hours divided by the dose prescribed then multiplied by 100 . The total dose over 24 hours was used in another study but was converted to an equianalgesic calculation . Another set of studies used a similar definition but specified percentages based on medication or type of prescription, such as an around-the-clock(ATC) regimen [13,15,16]. In 2 studies, adherence was measured based on chart review of yes/no questions posed about whether or not patients had taken medications as prescribed [3,15].
The measurements of adherence differed between studies. Four studies [4,12,14,16] used adherence as a primary outcome and the rest employed adherence as a facet of pain management [3,13,15]. The most frequent measure of adherence was self-report. The widely validated Morisky Medication Adherence Scale (MMAS) instrument was used in 3 of 7 studies [12,13,15]. Meghani and Bruner  utilized the modified MMAS plus a previously validated visual analog scale for doses of medication to assess adherence over week- and month-long intervals. One study used patient interviews to capture self-reporting of opioid prescription and opioid use. Additionally, the study used MMAS to further characterize the adherence measurements . Using a more objective method, Meghani et al  employed a microprocessor in the medication cap to determine the percentage of the total number of prescribed doses that were actually taken . The processor sensed when the bottle was open, which served as a proxy for taking medications at appropriate times.