Evaluation of a skin self examination attitude scale using an item response theory model approach

Ngadiman Djaja, Pip Youl, Joanne Aitken, Monika Janda, Ngadiman Djaja, Pip Youl, Joanne Aitken, Monika Janda

Abstract

Introduction: The Skin Self-Examination Attitude Scale (SSEAS) is a brief measure that allows for the assessment of attitudes in relation to skin self-examination. This study evaluated the psychometric properties of the SSEAS using Item Response Theory (IRT) methods in a large sample of men ≥ 50 years in Queensland, Australia.

Methods: A sample of 831 men (420 intervention and 411 control) completed a telephone assessment at the 13-month follow-up of a randomized-controlled trial of a video-based intervention to improve skin self-examination (SSE) behaviour. Descriptive statistics (mean, standard deviation, item-total correlations, and Cronbach's alpha) were compiled and difficulty parameters were computed with Winsteps using the polytomous Rasch Rating Scale Model (RRSM). An item person (Wright) map of the SSEAS was examined for content coverage and item targeting.

Results: The SSEAS have good psychometric properties including good internal consistency (Cronbach's alpha = 0.80), fit with the model and no evidence for differential item functioning (DIF) due to experimental trial grouping was detected.

Conclusions: The present study confirms the SSEA scale as a brief, useful and reliable tool for assessing attitudes towards skin self-examination in a population of men 50 years or older in Queensland, Australia. The 8-item scale shows unidimensionality, allowing levels of SSE attitude, and the item difficulties, to be ranked on a single continuous scale. In terms of clinical practice, it is very important to assess skin cancer self-examination attitude to identify people who may need a more extensive intervention to allow early detection of skin cancer.

Figures

Figure 1
Figure 1
Wright map/item person map of Skin Self-Examination Attitude Scale with the mean theta of persons on the left and mean theta of items on the right.

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