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Enhancing precision of the 16-item Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE-16) using Rasch methodology

Published online by Cambridge University Press:  19 November 2021

Quoc Cuong Truong ,
Carol Choo ,
Katya Numbers ,
Alexander G. Merkin ,
Perminder S. Sachdev Open the ORCID record for Perminder S. Sachdev [Opens in a new window] ,
Valery L. Feigin ,
Henry Brodaty Open the ORCID record for Henry Brodaty [Opens in a new window] ,
Nicole A. Kochan  and
Oleg N. Medvedev Open the ORCID record for Oleg N. Medvedev [Opens in a new window]
Quoc Cuong Truong
Affiliation:
School of Psychology, University of Waikato, Hamilton, New Zealand Faculty of Psychology, Vietnam National University Ho Chi Minh City, University of Social Sciences and Humanities, Ho Chi Minh City, Vietnam
Carol Choo
Affiliation:
College of Healthcare Sciences, Division of Tropical Health and Medicine, James Cook University, Queensland, Australia
Katya Numbers
Affiliation:
Centre for Healthy Brain Ageing (CHeBA), University of New South Wales, Sydney, New South Wales, Australia
Alexander G. Merkin
Affiliation:
National Institute for Stroke and Applied Neurosciences, Auckland University of Technology, Auckland, New Zealand Centre for Precise Psychiatry and Neurosciences, Kaufbeuren, Germany
Perminder S. Sachdev
Affiliation:
Centre for Healthy Brain Ageing (CHeBA), University of New South Wales, Sydney, New South Wales, Australia
Valery L. Feigin
Affiliation:
National Institute for Stroke and Applied Neurosciences, Auckland University of Technology, Auckland, New Zealand
Henry Brodaty
Affiliation:
Centre for Healthy Brain Ageing (CHeBA), University of New South Wales, Sydney, New South Wales, Australia
Nicole A. Kochan
Affiliation:
Centre for Healthy Brain Ageing (CHeBA), University of New South Wales, Sydney, New South Wales, Australia
Oleg N. Medvedev*
Affiliation:
School of Psychology, University of Waikato, Hamilton, New Zealand
*
Correspondence should be addressed to: Oleg N. Medvedev, School of Psychology, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand. Phone: + 64 7 837 9212. Email: oleg.medvedev@waikato.ac.nz.
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Abstract

Objective:

This study aimed to investigate psychometric properties and enhance precision of the 16-item Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE-16) up to interval-level scale using Rasch methodology.

Design:

Partial Credit Rasch model was applied to the IQCODE-16 scores using longitudinal data spanning 10 years of biennial 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 (MAS).

Participants:

The sample included 400 participants of the MAS aged 70 years and older, 109 out of those were diagnosed with dementia 10 years after the baseline assessment.

Measurements:

The IQCODE-16.

Results:

Initial analysis indicated excellent reliability of the IQCODE-16, Person Separation Index (PSI) = 0.92, but there were four misfitting items and local dependency issues. Combining locally dependent items into four super-items resulted in the best Rasch model fit with no misfitting or locally dependent items, strict unidimensionality, strong reliability, and invariance across person factors such as participants’ diagnosis and relationship to their informants, as well as informants’ age and sex. This permitted the generation of conversion algorithms to transform ordinal scores into interval data to enhance precision of measurement.

Conclusions:

The IQCODE-16 demonstrated strong reliability and satisfied expectations of the unidimensional Rasch model after minor modifications. Ordinal-to-interval transformation tables published here can be used to increase accuracy of the IQCODE-16 without altering its current format. These findings could contribute to enhancement of precision in assessing clinical conditions such as cognitive decline in older people.

Keywords

subjective cognitive complaintsmeasurementInformant Questionnaire on Cognitive Decline in the ElderlyRasch analysisreliability
Type
Original Research Article
Information
International Psychogeriatrics , Volume 36 , Special Issue 3: Issue Theme: Cognitive Trajectories in Later Life: Assessment Instruments and Empirical Data , March 2024 , pp. 166 - 176
Copyright
© The Author(s), 2021. Published by Cambridge University Press on behalf of International Psychogeriatric Association

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