Preventing Cognitive Decline and Dementia A Way Forward (2017) / Chapter Skim
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3 Methodological Improvements
3 Methodological Improvements
Pages 77-94
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From page 77... ...
on interventions to prevent cognitive decline and dementia. Examples of such challenges include initiation of interventions at later life stages that may be outside the optimal window; follow-up periods of insufficient duration; high attrition; small sample sizes and studies underpowered to detect changes in incidence of MCI and CATD; use of suboptimal and heterogeneous outcome measures and assessment tools; a focus on individual interventions when multiple 1 As discussed in Chapter 1, the scope of the study was limited to individual-level interventions.
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These methodological challenges limited the ability of the AHRQ systematic review to draw meaningful conclusions from many studies regarding the efficacy of interventions. To help ensure that future studies yield more definitive results, future investments in research on interventions for preventing cognitive decline and dementia would benefit greatly from efforts to rectify these common methodological shortcomings.
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In the Prevention of Dementia by Intensive Vascular Care (PreDIVA) trial, for example, which targeted vascular risk factors but failed to detect a reduction in all-cause dementia, the greatest effects were observed in those with uncontrolled blood pressure at baseline who adhered to the intervention (Moll van Charante et al., 2016)
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When race was incorporated at all among reported demographic factors in the studies included in the AHRQ systematic review, study populations often were found to be poorly representative of the diversity of the general population. Similar issues with underrepresentation can be observed with respect to such demographic characteristics as socioeconomic status and educational attainment.
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To ensure that public health messages promote interventions that are actually effective for the range of populations affected and can be targeted as appropriate, strengthening this evidence base by increasing the participation of underrepresented populations needs to be a priority in future research. Studies such as the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE)
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Studies recruiting adults across a range of age groups could help elucidate these life-course effects. The presumed latency period between onset of neurological changes and clinical symptoms has significant implications for the design of clinical trials, which if conducted in populations of middle-aged adults would require much longer follow-up periods to observe effects on CATD incidence and other cognitive outcomes.
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Effective strategies for retaining study participants identified in recent reviews include offering incentives (often financial) ; using systematic methods for contacting subjects and scheduling visits (e.g., follow-up reminders)
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Rigorous assessment of baseline status requires attention in future trials aimed at assessing the effect of interventions on preventing cognitive decline and dementia, particularly in the design of add-on studies. 3 To facilitate analysis, the AHRQ systematic review grouped neuropsychological tests into broad categories based on what they were being used to measure (e.g., executive function, memory)
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Challenges in interpreting results from add-on studies noted in the AHRQ systematic review -- unsophisticated outcome measures, a lack of baseline measurements, failure to assign subjects randomly -- generally arose from adding cognitive measures post hoc instead of building them carefully into the initial study design. Interinstitute communication within NIH and a standardized approach for a priori planning of cognitive add-on studies, including power considerations, would help overcome issues encountered in previous ancillary studies of cognition.
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All biomarkers reported in the studies included in the AHRQ systematic review were based on brain imaging techniques, specifically, magnetic resonance imaging (MRI) or positron emission tomography (PET)
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Given the potential of valid biomarkers to reduce the length and size of clinical trials (with associated impacts on feasibility and cost) , the committee supports continued efforts to further elucidate their relationship to cognitive outcomes.
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. Pragmatic trials may therefore be an efficient means of addressing knowledge gaps raised in the AHRQ systematic review, such as optimal blood pressure targets in antihypertensive trials and the comparative effectiveness of specific cognitive training applications.
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Recommendation 2: Methodological Improvements When funding research on preventing cognitive decline and demen tia, the National Institutes of Health and other interested orga nizations should improve the methodologies used in this field by supporting studies that to the extent possible • identify individuals who are at higher risk of cognitive decline and dementia and tailor interventions accordingly • increase participation of underrepresented populations to study intervention effectiveness in these populations • begin more interventions at younger ages and have longer follow-up periods • consistent cognitive outcome measures across trials to use enable pooling • integrate robust cognitive outcome measures into trials with other primary purposes • include biomarkers as intermediate outcomes • conduct large trials designed to test the effectiveness of an intervention in broad, routine clinical practices or community settings REFERENCES Alzheimer's Association.
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2014. Strategies to improve retention in randomised trials: A Cochrane systematic review and meta-analysis.
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2007. Racial and ethnic differences in cardiovascular disease risk factors: A systematic review.
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Clinical Trials 9(1)
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2007. Systematic review identifies number of strategies important for retaining study participants.
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Cochrane Database for Systematic Reviews 7:CD010386.
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