Supplementary Material for: Predictive Validity of Two Physical Frailty Phenotype Specifications Developed for Investigation of Frailty Pathways in Older People

<b><i>Background:</i></b> For investigating the relationship of frailty with physical, psychological, and social conditions on pathways, the frailty definition should ideally exclude these conditions. Based on the frailty phenotype, 2 candidate physical frailty specifications or instruments with 3 indicators, namely slowness, weakness, and exhaustion, and 4 indicators with addition of weight loss were previously developed, and had their construct and concurrent validity demonstrated. <b><i>Objective:</i></b> This study seeks to evaluate the predictive validity of 2 candidate physical frailty specifications with respect to death, functional impairment, and poor quality of life in older people. <b><i>Methods:</i></b> For 4,368 respondents aged 65-89 years from wave 2 of the English Longitudinal Study of Ageing, confirmatory factor analysis is performed for these 2 physical frailty specifications to obtain unique factor scores for each respondent. Prediction of death, basic and instrumental activities of daily living (BADL and IADL) difficulty, and poor quality of life (reverse of Control, Autonomy, Self-realization, and Pleasure [19 items] or CASP-19) 2 years later by factor scores for these 2 specifications is evaluated using standardized coefficients, c-statistics, and <i>r</i>² values from regression analyses. Their performance is compared with those of alternative specifications with 3 (slowness, weakness, and weight loss) and 5 indicators (slowness, weakness, exhaustion, weight loss, and low physical activity), and Frailty Index (FI). <b><i>Results:</i></b> For the 2 candidate specifications, an increase of 1 standard deviation (SD) predicts 50-57% increase in odds of death, 0.10-15 SD increase in change in BADL or IADL difficulty, and poor quality of life at 2 years. They predict these outcomes as well or better than the alternative specification with 3 indicators, but marginally worse than that with 5 indicators. Compared with FI, they predict death and poor quality of life similarly, but perform worse for functional impairment. Minor differences are observed across gender. <b><i>Conclusion:</i></b> Reasonable predictive validity of 2 candidate physical frailty specifications based on the frailty phenotype with 3 and 4 indicators is demonstrated for death, functional impairment, and poor quality of life. These findings offer evidence to support their suitability for employment in investigating frailty pathways in older people.

<b><i>研究背景：</i></b> 为探究衰弱与通路层面躯体、心理及社会状况的关联，理想的衰弱定义应排除上述因素。基于衰弱表型（frailty phenotype），既往已开发出两类候选躯体衰弱判定标准或工具：一类含3项指标，即步速缓慢、肌力减退与疲乏，另一类在此基础上增加体重下降，共4项指标，且二者的结构效度（construct validity）与同时效度（concurrent validity）均已得到验证。
<b><i>研究目的：</i></b> 本研究旨在评估上述两类候选躯体衰弱判定标准对老年人死亡、功能障碍及生活质量低下的预测效度。
<b><i>研究方法：</i></b> 本研究纳入英国老龄化纵向研究（English Longitudinal Study of Ageing, ELSA）第二波调查中4368名年龄介于65至89岁的受访者，针对上述两类躯体衰弱判定标准开展验证性因子分析（confirmatory factor analysis），为每名受访者生成唯一的因子得分。随后通过回归分析得到的标准化系数、C统计量（c-statistics）与决定系数（r²），评估两类标准的因子得分对2年后的死亡结局、日常活动基本能力（Basic Activities of Daily Living, BADL）与工具性日常活动能力（Instrumental Activities of Daily Living, IADL）障碍，以及生活质量低下（即控制感、自主性、自我实现与愉悦感量表[19条目版，简称CASP-19]的反向得分）的预测效果。同时将其与另外两类判定标准——含3项指标（步速缓慢、肌力减退与体重下降）的标准、含5项指标（步速缓慢、肌力减退、疲乏、体重下降与低体力活动）的标准，以及衰弱指数（Frailty Index, FI）——的预测性能进行对比。
<b><i>研究结果：</i></b> 针对上述两类候选判定标准，因子得分每增加1个标准差（standard deviation, SD），可预测2年后死亡风险升高50%~57%，BADL或IADL障碍程度提升0.10~1.5个标准差，同时生活质量低下的发生风险升高。二者对上述结局的预测效果优于或等同于含3项指标的替代标准，但略逊于含5项指标的替代标准。与衰弱指数（FI）相比，二者对死亡与生活质量低下的预测效果相当，但在功能障碍的预测上表现更差。不同性别间仅存在细微差异。
<b><i>研究结论：</i></b> 本研究证实，基于衰弱表型开发的、分别含3项与4项指标的两类候选躯体衰弱判定标准，对老年人的死亡、功能障碍及生活质量低下均具有合理的预测效度。上述研究结果为二者适用于老年人群衰弱通路相关研究提供了证据支持。