The purpose of this study was to investigate latent subgroups of SCD severity in the last year using BRFSS 2015-2020 and to identify associations with group membership by socio-demographic covariates. The analysis provided reasonable empirical evidence to support the hypothesis that discrete latent subgroups of SCD exist. Specifically, three discrete latent classes – Mild, Moderate, and Severe – represented indicators of SCD. To the best of our knowledge, this is the first study to use LCA to distinguish unobserved subgroups of SCD and demonstrate evidence of associated socio-demographic characteristics. Regarding Moderate SCD, age (65+ vs. 45-54; 55-64 vs. 45-54), employment (employed vs. retired), general health (excellent/very good/good vs. fair/poor), and having had a drink in the past 30 days are significantly negatively associated. Whereas income (<$15K vs. $50K+; $15-24K vs. $50K+; $25-49K vs. $50K+), unemployment (unemployed vs. retired), and having smoked at least 100 cigarettes in their lifetime are significantly positively associated with Moderate SCD. Regarding Severe SCD, race (non-Hispanic Black vs. non-Hispanic White; non-Hispanic Multiracial vs. non-Hispanic White; Hispanic vs. non-Hispanic White), education (<high school vs. college/tech school graduate; high school grad vs. college/tech school graduate; some college/tech school vs. college/tech school graduate), and income (<$15K vs. $50K+; $15-24K vs. $50K+; $25-49K vs. $50K+) are significantly positively associated. However, age (65+ vs. 45-54; 55-64 vs. 45-54), employment (employed vs. retired), general health (excellent/very good/good vs. fair/poor), and having had a drink in the past 30 days are significantly negatively associated with Severe SCD.
To the best of the authors’ knowledge, this is the first study to use a self-reported questionnaire to assess subgroups of cognitive impairment, which has utility for understanding the severity of SCD and implications for public health. This study extends the use of the SCD module for population-based surveillance of cognitive functioning. For example, indicators of SCD severity could advance surveillance as recommended in M-3 of the 3rd Edition: “State and Local Public Health Partnerships to Address Dementia: The 2018-2023 Road Map [9]. Understanding variability of SCD would improve program planning and resource allocation for state health systems and begin to address societal factors related to the burden of disease. Subsequently, one of the goals of the initiative is to diminish inequalities of Alzheimer's disease and related dementias in consideration of social determinants of health. Similar to prior research, our findings show disproportionate SCD based on race/ethnicity and socio-economic indicators (e.g., income and education) [34, 35]. However, we not only identify these characteristics as predictors of SCD but demonstrate that people who have low household income or educational attainment are most likely to have the worst symptoms. Discerning the nuances of SCD severity allows for improved tailoring of public health measures for the most affected communities. Furthermore, this study elucidates important findings regarding communication of SCD with a healthcare professional. Specifically, SCD severity is related to talking with a healthcare provider. The probability of discussing symptoms with a provider was over 50% for both the Moderate (53.4%) and Severe (61.8%) SCD groups, while only 28.8% for the Mild group. These findings not only provide further support for the Healthy People 2030 objective (DIA-03), but also identify target populations to improve the metric (i.e., “increase the proportion of adults with subjective cognitive decline who have discussed their symptoms with a provider”). All groups need to improve the proportion who have discussed symptoms with a provider. In particular, public health efforts should focus on the mild group with only roughly a quarter of these adults likely to speak with a healthcare professional. Even at the mild stage, early detection poses a great benefit to the affected individuals, caregivers, and overall healthcare costs [36]. Communication with a provider allows adults to eliminate other sources of dementia-like symptoms. If mild SCD develops into dementia, an early diagnosis gives patients more time to get symptomatic treatments, potentially enroll in clinical trials, as well as make legal and care arrangements with family. To improve this metric, public health efforts should be made to reduce the stigma surrounding discussing symptoms with family members, their healthcare providers, and to bring awareness for the need to have these discussions [37, 38].
Previous studies benefitted from the ability to assess cognitive profiles; however, many available assessments of cognition can be prohibitive for population surveillance due to the amount of resources necessary. The use of the cognitive decline module in tandem with the results of this study expands the utility of surveillance. Additionally, the current study includes an expanded list of socio-demographic covariates to prior research (i.e., age, sex, and education) which provides greater public health context to social and behavioral disparities associated with cognitive decline [15, 17, 39,40,41]. Among the two studies which used the prediction model to assess associations with group membership, our study found similar results for education yet disparate findings for age and sex [15, 40]. In contrast to our study, each found sex to be significantly related to latent class membership [15, 40]. These studies found males had significant relationships with cognitive profiles (positive: attention/ construction symptoms; negative: memory symptoms) whereas females were significantly positively associated mild to severe impairment generally [15, 40]. Considering these findings, there may remain differences in cognitive profiles within our latent subgroups. Separately, Davidson et al. (2010) and Scheltens et al. (2016) both found low education to be significantly associated with greater severity of Alzheimer’s. SCD is frequently a feature of Alzheimer’s disease and these results contribute to the evidence that educational attainment is an important modifiable risk factor for prevention of future cognitive impairment and disease progression. Lastly, contrary to Davidson’s findings, our study showed that younger age is associated with moderate and severe SCD [40]. While opposing the logical expectation, one reason for members of the Moderate or Severe SCD groups to more likely be younger could be due to stigma of failing cognition affecting the way older respondents report the frequency of SCD [38, 42]. However, it is also possible that respondents who have a higher probability of developing Alzheimer’s disease or a dementia-related disease, such as those with a lower educational attainment, are experiencing cognitive decline at a younger age [43, 44].
There are limitations to this study that should be considered. First, our sample only includes community-dwelling individuals and may exclude those with limitations associated with cognitive functioning. Second, coding respondents who reported never or rarely needing assistance with day-to-day activities (n=37,341, 68%) as “never” for item 4 could affect the probabilities for the Never/NA response. A sensitivity analysis demonstrated similar LCA model fit results with and without imputation. Final model selection was not affected. Third, when interpreting the results of this analysis, only respondents who experienced SCD were included. In post hoc analyses, the model was tested on the full sample as well. Restricting the sample to those with SCD improved model fit and conceptual distinction of classes. There are strengths to this study. First, using latent class analysis is superior to other common methods accounting for measurement error to improve precision of estimates [45]. And, second, the previous studies yield prudent findings through diagnostic means but are limited by cost and logistical feasibility for population-level surveillance. Specifically, there is practical use for the three latent indicators of severity from our findings. Rather than continuing as item-by-item analysis of this module, latent classes more easily quantify the severity of SCD. Future research is necessary to expand this work. For example, research should investigate the neurological differences between members of the Mild, Moderate, and Severe SCD groups.
In summary, latent class analysis has useful applications for population-level surveillance measures. This study demonstrated respondents of the BRFSS’ cognitive decline module cluster into three discrete latent subgroups regarding the severity of SCD (Mild, Moderate, and Severe). Socio-demographics were associated with membership in each group. Although the cognitive decline module is not a diagnostic tool, using these discrete latent groups can provide clarity for SCD prevalence in the population. Specifically, the use of the three latent subgroups, rather than item-by-item analysis, allows for a more intuitive understanding of the public health burden. These study findings could easily be utilized in an applied or academic setting. For example, opposed to assessing discrete items, a holistic approach to more fully understand the national and state-level epidemiology of SCD is now possible. While individual items provide important information regarding SCD, the overall health burden has historically been more challenging to interpret. Using this new LCA indicator, researchers can easily quantify SCD severity nationally or within their locale. Further, this method allows for facile identification of respondent characteristics based on SCD severity, and it can also be used to consider spatial distribution in various geographies. Considering the progression from mild cognitive impairment to dementia-related illnesses, it is particularly important for public health to continue to improve the ability to monitor the aging health of our population and it’s effect on our communities [46]. The labor demand of caregivers for ADRD adults has negative impacts on physical and mental health. Additionally, caregivers are insufficiently remunerated with a share of roughly 20 hours per week per caregiver being unpaid [36]. Further, the direct cost of Alzheimer’s disease in 2019 is $290 billion with 67% covered by Medicare and Medicaid [36]. Through improved cognitive decline surveillance and response, there is potential to stymie the substantial societal and financial impact of Alzheimer’s disease and dementia-related disorders.