Application of Rasch Analysis to Timed Instrumental Activities of Daily Living in Low Vision: A Validation Study

Area of Science:

• Rehabilitation Science
• Low Vision Research
• Psychometrics

Background:

• Functional outcome measures are crucial for assessing rehabilitation effectiveness in low vision patients.
• Evaluating these measures in real-world settings, such as patients' homes, enhances their relevance.
• Rasch analysis provides a robust framework for validating measurement tools.

Purpose of the Study:

• To validate Rasch analysis for a performance-based low vision outcome measure.
• To assess the real-world relevance of functional outcome measures by evaluating them in patients' homes.
• To determine the utility of both performance time and error data in Rasch analysis.

Main Methods:

• Rasch analysis was applied to performance time and error count data from 161 low vision patients performing Timed Instrumental Activity of Daily Living (TIADL) tasks at home.
• Internal validity was assessed using accuracy and precision of estimated measures.
• External validity was evaluated by comparing TIADL measures with those from the Activity Inventory.

Main Results:

• Performance time data yielded well-targeted measures with good internal validity.
• Error count data showed poor targeting and higher standard errors, indicating a ceiling effect (72% error-free trials).
• Time-based TIADL measures demonstrated weak correlation with Activity Inventory measures (R=0.19).

Conclusions:

• Performance time-based measures of functional ability in home environments demonstrate good internal and external validity.
• The infrequency of errors in TIADL tasks limits the use of error data for measuring rehabilitation outcomes due to a ceiling effect.
• Rasch analysis is a suitable method for validating performance-based outcome measures in real-world settings.