Applying generalizability theory to examine assessments of subjective cognitive complaints: whose reports should we rely on – participant versus informant?

Abstract

Objectives: This study aimed to apply the generalizability theory (G-theory) to investigate dynamic and enduring patterns of subjective cognitive complaints (SCC), and reliability of two widely used SCC assessment tools. Design: G-theory was applied to assessment scales using longitudinal measurement design with five assessments spanning 10 years of follow-up. Setting: Community-dwelling older adults aged 70–90 years and their informants, living in Sydney, Australia, participated in the longitudinal Sydney Memory and Ageing Study. Participants: The sample included 232 participants aged 70 years and older, and 232 associated informants. Participants were predominantly White Europeans (97.8%). The sample of informants included 76 males (32.8%), 153 females (65.9%), and their age ranged from 27 to 86 years, with a mean age of 61.3 years (SD = 14.38). Measurements: The Memory Complaint Questionnaire (MAC-Q) and the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE). Results: The IQCODE demonstrated strong reliability in measuring enduring patterns of SCC with G = 0.86. Marginally acceptable reliability of the 6-item MAC-Q (G = 0.77–0.80) was optimized by removing one item resulting in G = 0.80–0.81. Most items of both assessments were measuring enduring SCC with exception of one dynamic MAC-Q item. The IQCODE significantly predicted global cognition scores and risk of dementia incident across all occasions, while MAC-Q scores were only significant predictors on some occasions. Conclusions: While both informants’ (IQCODE) and self-reported (MAC-Q) SCC scores were generalizable across sample population and occasions, self-reported (MAC-Q) scores may be less accurate in predicting cognitive ability and diagnosis of each individual.

Clinical utility of self-reported and informant-reported cognitive complaints in older adults

“…In conclusion, there is growing recognition of the utility and limitations of self-and informantreported SCCs in identifying those who may be at risk of developing objective declines in the future. The work by Truong et al (2022) adds support for the potential utility of SCCs when measured by reliable and generalizable measures. Their findings and the extant literature suggest that both self-and other-reported SCCs can be important parts of a comprehensive, integrated assessment of an older adult's cognitive and mental health status.…”

“…The study by Truong et al (2022) expands the existing body of SCC literature by evaluating dynamic and enduring patterns of SCCs reported by patients and informants over a 10-year span. In a large sample of community-dwelling older adults from Australia, the authors used generalizability theory to examine the overall reliability of two widely used measures of self-and informant-reported SCCsthe Memory Complaint Questionnaire (MAC-Q) and the Informant Questionnaire on Cognitive Decline in the Elderly (IQ-CODE).…”

Establishing conversion of the 16‐item Informant Questionnaire on Cognitive Decline in the Elderly scores into interval‐level data across multiple samples using Rasch methodology

“…13 Results from the MAS showed that informant IQCODE scores were more accurate in predicting cognitive performance and incident dementia compared to self-reported MAC-Q scores. 5 Moreover, self-reports are subject to various biases such as the individual's mood (e.g. depression, anxiety), personality traits (e.g.…”

A novel approach to investigate depression symptoms in the aging population using generalizability theory.

“…Generalizability theory (G theory) is an advanced statistical method that estimates all possible error variances and their influences on the overall reliability of a measure (Truong et al, 2020(Truong et al, , 2021. G theory is increasingly being used to investigate the psychometric properties of measurement tools and to distinguish dynamic and enduring symptoms.…”