The present study examined associations of cognitive performance and informant reports of cognitive decline with the probabilities of CIND and dementia among African Americans and whites. We found that a better cognitive performance, as assessed by CERAD TS, was associated with lower odds of CIND and dementia among both African American and white participants, with similar odds ratios between groups for each of these diagnoses. We also found that informant reports of greater cognitive decline on IQCODE were associated with higher prevalent dementia odds among both African Americans and whites. For a diagnosis of CIND, however, greater informant reports of cognitive decline were associated with increased odds of this condition among whites, but not African Americans. These results suggest that informant reports of cognitive decline, as assessed by IQCODE, may differ between African Americans and whites for the detection of the milder cognitive and functional impairments of CIND. These results were independent of the covaried effects of age, education, and gender.
The mean differences in CERAD TS between African Americans and whites are consistent with previous studies finding that African Americans generally have lower scores on neuropsychological measures used in the assessment of cognitive impairment and dementia [12
], including some tests within the CERAD battery [10
]. In many cases, the evidence demonstrates that racial differences in cognitive performance are strongly associated with educational attainment, literacy, and quality of education. However, it may also be the case that educational variables are a proxy for acculturation and broader sociocultural factors [7
]. Although racial and ethnic differences in neuropsychological test performances may raise concerns about diagnostic disparities, the slopes of mean CERAD TS scores were similar in each diagnostic category between African Americans and whites. Moreover, we found that the relative risks of CIND and dementia associated with CERAD TS performance were comparable among blacks and whites, when controlling for the effects of education, age, and gender.
With respect to our finding that IQCODE was associated with a diagnosis of CIND among whites but not African Americans, our results suggest that: 1) African American informants may be less
inclined to report mild cognitive changes, 2) whites may be more
inclined to report mild cognitive changes, or 3) both conditions may exist. Although there is limited research on how African American and white informants differ in perceiving cognitive changes as a function of magnitude or diagnosis, one study did find that African American caregivers overrated the care recipient’s cognitive function, whereas white caregivers underrated cognitive ability [13
]. Although most participants in the present study were independent and community-dwelling, it may be possible to compare our findings with those in the dementia caregiver literature, where the majority of studies found that African American caregivers reported less depression [44
], more positive appraisal [46
], less stress over behavioral disturbances [44
], and a lower caregiver burden [49
] than did white dementia caregivers. Along with the present findings using IQCODE, this research suggests that cultural attitudes toward cognitive impairment and caregiving among African Americans and whites may produce different informant reports of cognitive decline. Previous studies of IQCODE in multiple countries suggested limited cultural differences in IQCODE, but those studies typically evaluated dementia within relatively homogenous cultural groups in their respective samples. We are not aware of a similar comparison of two cultural groups based on IQCODE for both cognitive impairment and dementia within the same sample, as was the case in the present study. More research is needed on IQCODE and other informant reports of cognitive decline in samples that allow for comparison of multiple cultural groups and different levels of cognitive decline. This issue is also relevant in other countries where differences in education, acculturation, and other factors may influence perspectives on cognitive change in the elderly.
We believe the current results have implications for the detection of CIND and dementia in clinical contexts, and for cognitive screening in population-based research. Although some normative values specific to African Americans exist for the CERAD battery [10
], they do not exist for the CERAD TS, and there is a general lack of screening instruments for dementia and cognitive impairment from which appropriate cutoffs could be established with respect to age, education, and ethnicity. Informant reports such as IQCODE can potentially improve the community-based screening of cognitive impairment, because they are time-efficient and useful when cognitive testing is not feasible, and positive screening may be used to identify the need for additional neuropsychological evaluation. Similarly, although our results suggest that IQCODE may be useful in screening for dementia among both African Americans and whites, an independent sample is needed to establish appropriate values for sensitivity and specificity in each cultural group. In the case of cognitive impairment in the absence of dementia, our results suggest that IQCODE may be useful in identifying cognitive changes consistent with CIND among whites, but more research is needed to understand the factors that influence scores among African Americans.
This study contains some potential limitations. For instance, the agreement between CERAD TS and clinical diagnoses may not be entirely unexpected, because these data were among the information that was considered in assigning clinical diagnoses in ADAMS. The IQCODE, on the other hand, was completed at the time of the study visit, but was not used in the diagnostic process. With respect to CERAD TS, we emphasize that: 1) the CERAD battery was presented as separate test components at the time of diagnosis, with no reference to the CERAD TS, which was calculated solely for the purposes of the present study; and 2) the CERAD battery was one element of a more extensive neuropsychological examination that included additional assessments of memory, attention, language, and executive function. In addition, the neuropsychological examination was one aspect of a comprehensive clinical assessment that included a clinical and medical history, other informant reports of cognition and functional performance, applicable medical records, and a brief neurologic examination. The totality of this information was used by a consensus panel of psychologists and physicians, who judged these data with respect to formal diagnostic criteria and from the perspective of their own specializations and clinical experience. Thus, although components of the CERAD TS performance were known in some form at the time of diagnosis, it is unlikely that the CERAD TS was overly influential in the diagnostic process.
We also note a correlation among some of the predictor variables, which may have accounted for unexpected trends of increased odds of cognitive impairment in association with higher level of education in models with the CERAD TS. This finding is not consistent with our univariate results, and is likely attributable to the influence of educational level on CERAD TS. Correlations between educational level and neuropsychological tests are difficult to avoid, which highlights a need for neurocognitive tests that are sensitive to cognitive impairment, while decreasing the influence of education on test outcomes.
An important issue remains in terms of the generalization of our results. The sample size available to examine the risk of cognitive impairment among African Americans was small for models with three diagnostic groups and three covariates. It is possible that with a larger sample size, we might have detected a significant association of IQCODE with predicting CIND among African Americans. With a larger sample size, we may also have been able to explore the trend of a decreased likelihood of CIND among white women in models with IQCODE, which may reflect an interesting interaction of both race and sex in informant reports of cognitive function. We also lacked the sample size to evaluate subtypes of CIND and dementia, which are heterogeneous in terms of clinical course and presentation, and which may have had different individual associations with CERAD TS and IQCODE. Only a few population-based studies in the research literature had a large enough sample size to examine subtypes of CIND and dementia diagnoses among African Americans relative to whites or other racial and ethnic groups in the United States, and many of these studies were regionally and culturally specific. This highlights the need for population-based studies of cognitive impairment and dementia with sufficient samples sizes of nonwhite populations, but the greatest utility would arise from a study on a nationally representative scale, using a single methodology of assessment and diagnosis. Such a study might not only promote an understanding of the questions raised by the present study, but might also examine the contributions of multiple demographic, cultural, and medical influences that are important in understanding racial and ethnic disparities in outcomes of cognitive impairment and dementia. A better understanding of racial and ethnic disparities in cognitive impairment, dementia, and other age-related medical conditions will be needed to effectively meet the needs of the aging, diverse United States population.
The present study found that CERAD TS identified dementia and CIND in both whites and African Americans, but that IQCODE provided divergent results between whites and African Americans when cognitive impairment was below the threshold of dementia. Additional research is needed to understand how cultural perceptions may influence the perception of cognitive function when the presentation is emergent or heterogeneous in nature.