Validity of the Adaptation to Age-related Vision Loss Scale in an Australian Cataract Population

Abstract

PURPOSE:The Adaptation to Age-related Vision Loss (AVL) scale was developed to measure the adjustment of older adults who are adapting to late-life vision loss. The purpose of this study was to assess whether the AVL scale satisfies the Rasch model in a cataract population. METHODS:The 24-item AVL scale (18 negatively and 6 positively coded) was mailed to 436 cataract patients for self-administration whilst they were on the waiting list for cataract surgery at the Flinders Eye Centre, Adelaide, South Australia. Rasch analysis was performed to determine whether the items were measuring a single construct (unidimensionality) as examined with fit statistics and principal components analysis (PCA) of the residuals. The ability of the scale to distinguish between the levels of adaptation of the participants (person separation) was investigated, with a value ≥ 2.0 established as the minimum acceptable. RESULTS: The AVL scale was unable to differentiate sufficiently between participants' levels of adaptation, indicating poor person separation. One item did not fit the construct, causing misfit. Furthermore, the five positively worded items did not appear either to measure the same construct as other items, resulting in lack of unidimensionality evidenced by PCA. Following the deletion of these items, the AVL scale was one-dimensional but a single item continued to misfit, so it had to be deleted, resulting in an 18-item AVL scale. Even so, the discriminating abilities of the scale continued to be poor. CONCLUSIONS: The AVL scale is not an appropriate measure of adaptation to vision loss in a cataract population. KEY WORDS: Rasch analysis; adaptation to Age-related Vision Loss Scale; cataract; Australia. RESUMEN OBJETIVO: La Escala de adaptación a la pérdida visual relacionada con la edad (o sus siglas en inglés, AVL) se desarrolló para medir el ajuste de los adultos de edad avanzada ante la pérdida visual que suele aparecer en esta fase de la vida. El propósito de este estudio era evaluar si la escala AVL también se ajusta al modelo de Rasch en una población de personas con cataratas. MÉTODOS: Se envió por correo postal el cuestionario correspondiente a la escala AVL de 24 elementos (18 codificados negativamente y 6 positivamente) a 436 pacientes del Flinders Eye Centre, Adelaida, South Australia (Australia) que se encontraban en la lista de espera para cirugía de cataratas. Los pacientes debían completar el cuestionario y devolverlo por correo. Se realizó un análisis de Rasch de los resultados para determinar si todos los elementos de la escala están midiendo un único parámetro (unidimensionalidad). Esto se llevó acabo utilizando estadísticos de ajuste así como análisis de componentes principales (o sus siglas ACP) de los residuos. Se evaluó la capacidad de la escala para discriminar entre los distintos niveles de adaptación de los participantes (denominada separación o fiabilidad), estableciendo un valor umbral de 2,0 como el valor mínimo aceptable. RESULTADOS: La escala AVL no fue capaz de diferenciar de fo...

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