Functioning score transformation table.

Background
Beyond mortality and morbidity, health statistics would benefit from reporting information on functioning, the third health indicator. The objective of this article is to use data from the Swiss Survey of Health, Ageing and Retirement in Europe (SHARE) to exemplarily create a psychometrically sound and valid metric of functioning for the ageing population living in Switzerland.
Methods
Partial Credit Model (PCM) analysis, including analysis of targeting, item fit, local item dependencies (LID), unidimensionality, and differential item functioning (DIF), tested the psychometric properties of selected items. The DIF analysis investigated the invariance of item difficulties across sex and age groups, country, language, and the assessment Wave.
Results
Data from 34,092 individuals aged 50 years and older was selected across assessment Waves of SHARE. The analysis showed that a functioning metric can be constructed with a total of 33 functioning items. Items showed LID and multidimensionality initially, which was solved with a testlet approach. Aggregation into testlets resulted in good fit, unidimensionality, no LID, and no DIF for sex, country, language, and the assessment Wave. Some DIF is found for age groups. The analysis also showed that the selected items target higher levels of problems in functioning than observed in the study population.
Conclusions
A functioning metric can be constructed from selected functioning items of SHARE. The metric provides a sound interval-scaled score that can be used for longitudinal analyses of ageing in Switzerland and neighboring countries or as an indicator of the level of functioning in an ageing population.

# 背景
除死亡率与发病率外，健康统计若纳入健康功能（functioning）这第三类健康指标，将更具学术与实践价值。本文旨在借助欧洲健康、老龄化与退休调查（Swiss Survey of Health, Ageing and Retirement in Europe, SHARE）的瑞士相关数据，为瑞士居住老年人群构建一项心理测量学上稳健且有效的健康功能量化指标，作为示例研究。

# 方法
本研究采用部分计分模型（Partial Credit Model, PCM）开展分析，涵盖项目靶标分析、项目拟合度检验、局部项目相依性（local item dependencies, LID）检验、单维性检验以及项目功能差异（differential item functioning, DIF）检验，以评估所选取条目的心理测量学属性。其中项目功能差异（DIF）分析旨在检验项目难度在不同性别、年龄组、国家、语言以及评估波次（assessment Wave）间的不变性。

# 结果
本研究从SHARE各评估波次中筛选出34092名50岁及以上受访者的数据。分析结果显示，可基于共计33项健康功能条目构建健康功能量化指标。初始分析表明，所选条目存在局部项目相依性与多维性问题，通过题组（testlet）分析法可有效解决该类问题。将条目聚合为题组后，模型拟合效果良好，且满足单维性要求，未出现局部项目相依性，在性别、国家、语言及评估波次上均未检测到项目功能差异；仅在年龄组间存在少量项目功能差异。此外，分析还发现，所选条目所针对的健康功能问题严重程度高于本研究人群的实际观测水平。

# 结论
本研究可基于SHARE的精选健康功能条目构建健康功能量化指标。该指标可生成稳健的等距量表得分，可用于瑞士及周边国家的老年人群健康功能纵向分析，亦可作为老年人群健康功能水平的评估指标。