Cross-cultural adaptation and validation of the Amsterdam Instrumental Activities of Daily Living questionnaire short version German for Switzerland

Abstract

Background: Instrumental Activities of Daily Living (IADL) limitations are associated with reduced health-related quality of life for people with mild cognitive impairment (MCI). For these people, the assessment of IADL is crucial to the diagnostic process, as well as for the evaluation of new interventions addressing MCI. The Amsterdam IADL Questionnaire Short Version (A-IADL-Q-SV) is an established assessment tool with good psychometric properties that has been shown to be robust to cultural differences in Western countries. The aims of this study were to: (1) cross-culturally adapt and validate the A-IADL-Q-SV for the German-speaking population of Switzerland; (2) investigate its cultural comparability; and (3) evaluate further psychometric properties.

Methods: The A-IADL-Q-SV German was pretested on clinicians and participants in a memory clinic setting. The psychometric properties and cultural comparability of the questionnaire were investigated in memory clinic settings including participants with MCI or mild dementia, as well as participants with normal cognition recruited from the community. Item response theory (IRT) was applied to investigate measurement invariance by means of differential item functioning to assess item bias. Additionally, the test-retest reliability on scale level, the construct validity through hypothesis testing and the discriminant validity of the A-IADL-Q-SV German were evaluated.

Results: Ninety-six informants of participants with normal cognition, MCI or mild dementia completed the A-IADL-Q-SV German. The basic assumptions for IRT scoring were met. No meaningful differential item functioning for culture was detected between the Swiss and Dutch reference samples. High test-retest reliability on scale level (ICC 0.93; 95% CI 0.9-0.96) was found. More than 75% of the observed correlations between the A-IADL-Q-SV German and clinical measures of cognition and functional status were found to be in the direction and of the magnitude hypothesized. The A-IADL-Q-SV German was shown to be able to discriminate between participants with normal cognition and MCI, as well as MCI and mild dementia.

Conclusions: The A-IADL-Q-SV German is a psychometrically robust measurement tool for a Swiss population with normal cognition, MCI and mild dementia. Thus, it provides a valuable tool to assess IADL functioning in clinical practices and research settings in Switzerland. Trial registration This study was registered retrospectively in July 2019 on ClinicalTrials.gov (NCT04012398).

Keywords: Amsterdam IADL questionnaire; Assessment; Cross-cultural validation; Elderly people; Instrumental Activities of Daily Living (IADL); Mild cognitive impairment (MCI); Mild dementia.

Fig. 1

Latent trait distributions and test characteristic curves. The red dotted lines show the Swiss population and the solid black lines the Dutch reference group. a Latent trait distributions for the Dutch reference sample and the Swiss sample. b Test characteristic curves including all items for the Dutch reference sample and the Swiss sample. c Test characteristic curves including the three items with differential item functioning for the Dutch reference sample and the Swiss sample

Fig. 2

Bland and Altman plot including all participants. The X-axis shows the means of the T-scores of the two measurement time points and the Y-axis the differences in means of the T-scores between the two measurements. The horizontal red dashed line represent the mean difference, the dark blue dashed lines the 95% CI of the mean difference, the blue dashed lines the lower and upper limits of agreement, and the black dotted line the regression line between the mean of the T-scores and difference in the means of the T-scores. Triangles represent participants with mild cognitive impairment or mild dementia and circles participants with normal cognition

Fig. 3

Bland and Altman plot of the subgroups. The horizontal red dashed line represent the mean difference, the dark blue dashed lines the 95% CI of the mean difference, the blue dashed lines the lower and upper limits of agreement, and the black dotted line the regression line between the mean and difference in the means. a The X-axis shows the means of the T-scores of the two measurement time points and the Y-axis the differences in means of the T-scores between the two measurements. b Note this figure is based on the rankits of the T-score in participants with normal cognition. The X-axis shows the means of rankits of the T-scores of the two measurement time points and the Y-axis the differences in means of rankits of the T-scores between the two measurements

Fig. 4

T-Scores of the three diagnostic groups