The methodology described in this report presents a novel approach to better quantifying the burden on the healthcare system represented by the spouses of patients with AD or other debilitating chronic conditions. By linking spouses with shared CANs in the Medicare 5% sample and creating a control spouse cohort, the impact of an AD diagnosis on the spousal dyad was explored cross-sectionally and longitudinally. The temporal association between the patients’ AD diagnosis and the increase in Medicare expenditures for their spouses as compared to controls illustrates the strength of our method. That relationship underscores the impact of the AD diagnosis on spouses’ health, independent of a couple’s joint lifestyle or other common factors that might contribute to the AD spouses’ medical costs. The ability to track the details of cost and service utilization on a monthly basis is yet another advantage to utilizing Medicare records rather than relying on self-reports of healthcare utilization. Despite such benefits, several complex issues concerning the validity of our approach deserve further examination.
AD ascertainment through Medicare claims
Medicare claims records are robust since they list all types of services, including those performed on both an inpatient and outpatient basis. Moreover, the need to receive payment for their services disciplines providers to be complete when filing these claims.
Concern nonetheless remains about the reliability of using Medicare claims to summarize the impact of AD and other dementias on resource utilization. Even when an AD-related diagnosis is appropriate, providers faced considerable hurdles obtaining Medicare payment during our study period [35–37]. The literature suggests a physician and hospital bias toward filing claims based on more clear-cut and easily reimbursable diagnostic codes related to patients’ physical comorbidities rather than on patients’ cognitive impairments [35, 37].
Two studies have examined Medicare data contemporaneous with our study period [38, 39]. One study included patients with presenile/senile dementia diagnostic codes in their claims as well as those with 331.0 for AD . It used only survey responses to validate these diagnoses. The other study  carried out formal clinical assessments to determine who had AD, other forms of dementia or mild cognitive impairment in the Aging Demographics and Memory Study (ADAMS) cohort of 856 older Americans.
After reviewing the cohort’s Medicare claims, the ADAMS investigators concluded that the sensitivity and specificity of those claims for capturing an AD diagnosis was respectively, 64% and 95%. By comparison, Medicare claims sensitivity and specificity for all-cause dementia was 85% and 89%. Identifying AD patients through Medicare claims is thus a very selective strategy but misses a substantial percentage of patients, probably those with atypical or mild cases.
The present study’s AD population represents a core of easily identified cases receiving recurring AD-related care. Broadening our AD definition could have increased the study population by as much as two-fold [40, 41], but including less severe and more ambiguous cases of AD would have weakened our ability to investigate AD-specific spillover effects on spousal health. Comparing the relationship between various coding patterns and clinical signs of cognitive impairment would help in the development of more accurate algorithms for parsing Medicare claims. That examination is outside our current scope.
Characteristics of the identified spouses
Since the goal of this study was to evaluate the secondary effects of AD on spouses, our ability to identify only a quarter of the potential spouses becomes important. In making this identification, we took advantage of a wrinkle in the Medicare beneficiary numbering system that identifies spouses without their own retirement accounts through their partners’ Social Security numbers. Medicare automatically includes both such spouses when constructing its 5% beneficiary sample.
Our method identified many primary Medicare beneficiaries who were the spouses (primarily husbands) of dependent partners diagnosed with AD. It omitted households in which both spouses had large enough prior earnings to qualify for Medicare on their own. Women with substantial work histories make up a growing proportion of Medicare beneficiaries, however, and study of spousal effects in two wage-earner couples is becoming more important.
It is possible that spouses with substantial work experience react more resiliently to their partner’s AD. They may have greater financial resources and feel more self-empowered than a spouse with little outside work experience. Conversely, a spouse who has spent a majority of time at home may be more familiar with and/or less burdened by home-based caregiving. Our study could not be sensitive to these possibilities.
An additional 25% of elderly Medicare spouses could be captured when they apply for widow benefits and emerge as married beneficiaries in the Medicare denominator (demographic) data files . Employing this method for spousal healthcare cost and utilization studies would require claim records for the entire Medicare elderly population during the study years plus demographic data for many years beyond. These files were not available to us.
A still more complete spousal identification would involve linking AD case information with address records for each year and matching cohabitants via their common addresses. This method would create a complete file that includes all cohabiting partners, whether they are married or not, while excluding married couples who are separated (a small proportion of elderly spouses ). We could then describe in depth the differences between spouses according to their previous work history.
Distributing Medicare address files raises privacy concerns, however, and CMS usually does not release this information. Even if the agency did allow access, the address records would present a significant processing challenge because they lack a standard format. Another challenge would be excluding elderly cohabitants who are simply relatives or roommates rather than spouses.
Spouses first or caregivers?
Identifying the entire spousal population solely through Medicare claims would still yield no practical way to determine the extent of their caregiving role. A considerable literature on AD and other disabilities does document that cohabiting spouses are usually the chief caregiving resource when they are not incapacitated themselves [12, 42–45]. National U.S. surveys have found that up to 80% of spouses living with elderly disabled partners devote substantial time to caregiving tasks [44, 45].
This overall spousal caregiving burden does not provide the basis for individual risk analysis, however, and even knowing the caregiving obligations of each spouse would be insufficient to predict their health risk. The nature of a couple’s relationship influences whether caregiving is experienced as fulfilling or a strain, and that subjective interpretation in turn can affect health and mortality [46–48]. The nature of the spousal relationship also independently affects spouses’ mortality when their partners become seriously ill or die [11, 49]. These observations are conspicuously true of cognitive impairment: Dementia in one spouse greatly increases the risk of dementia in the other, and spousal closeness decreases dementia progression in the affected partner [50, 51].
Spouses’ interrelated health outcomes may be influenced by a couple’s shared environment as well as to their emotional ties. It will not be possible to capture the individual, granular details of this phenomenon through claims records alone. Our method nonetheless allows researchers to show the population-level patterns that mirror the underlying individual interactions.
The question also arises as to whether spouses of patients with other chronic diseases would experience similar increases in healthcare costs. There are rare examples of this phenomenon existing for other disease states  or in association with widowhood from decedents of other chronic conditions . The goal of our study was to find a connection between spouses’ healthcare status and their partners’ AD diagnosis while statistically controlling for a broad spectrum of impairments with the JFI. This temporal association is illustrated in Figure 1. One can speculate that AD’s particular behavioral and cognitive effects are especially stressful for spouses, both emotionally and in terms of caregiving burden. It will be a fruitful line of research to compare the spousal results presented in Table 4 and Figure 1 with results obtained for other chronic diseases. The methods we establish here can form the basis for such research.
Comprehensiveness of costs
Medicare FFS data includes claims related to outpatient and inpatient services, short-term skilled nursing home stays, hospice, select home health services, physician/medical professional services, and durable medical equipment. It does not include certain behavioral health services, many home-care services, or long-term nursing home residencies. Other omissions are payments by private supplementary insurance, Medicaid or pre-2006 outpatient pharmacy costs. So long as the study focuses on comparing relative costs in carefully defined exposed and unexposed cohorts, restricting the quantitative results to Medicare FFS expenditures will not make a qualitative difference in its conclusions. Analyses of data linked from the different sources described above would further advance the research reported here.