Psychometric properties of the Nottwil Environmental Factors Inventory Short Form

Abstract

Objectives: To examine the psychometric properties of the Nottwil Environmental Factors Inventory Short Form using Rasch analysis; to determine its construct validity and internal consistency; and to develop a metric for scoring.

Design: Cross-sectional psychometric study. Construct validity of the Nottwil Environmental Factors Inventory Short Form, including model fit, person and item fit, local item dependence, dimensionality, and differential item functioning (DIF), was investigated with Rasch analysis. Internal consistency was assessed with Cronbach alpha and item-total correlations.

Setting: Community.

Participants: Swiss residents aged >16 years and living with traumatic or nontraumatic spinal cord injury (SCI) (N=1549).

Interventions: Not applicable.

Main outcome measure: The Nottwil Environmental Factors Inventory Short Form, a 14-item questionnaire developed to assess perceived impact of environmental barriers on participation.

Results: Local dependencies between items addressing a similar content could be solved by creating a testlet. With 1 testlet there was strong evidence for unidimensionality of the Nottwil Environmental Factors Inventory Short Form. Although person-item targeting revealed a floor effect, indicating few perceived environmental barriers to participation in the Swiss SCI population, the item fit was good. Only a few items presented DIF. The Nottwil Environmental Factors Inventory Short Form showed good internal consistency (α=.82).

Conclusions: This psychometric analysis supports the use of the Nottwil Environmental Factors Inventory Short Form to evaluate perceived environmental barriers to participation in persons with SCI living in the community.

Keywords: Environment; International Classification of Functioning, Disability and Health; Psychometrics; Rehabilitation; Social participation; Spinal cord injuries.