Scale for developmental dyslexia screening: evidence of validity and reliability

Purpose: To investigate the empirical validity and reliability of a screener for risk of developmental dyslexia (DD) by elementary school teachers. Methods: The scale was tested with 12 teachers who answered questions about their students (95 students total, all in the third year of elementary school); the students, in turn, performed reading and writing tasks which were used to investigate the association between screening scores and performance. The following analyses were carried out: (1) factor analysis; (2) internal consistency; (3) relationship between each scale item and the construct of interest, as measured by item response theory (IRT); (4) correlation of each scale item with external variables (reading and writing tests); and (5) the temporal stability of teachers' evaluations. Results: The analyses showed: (1) one factor was extracted; (2) strong internal consistency - the items in the scale are good indicators for screening of this construct; (3) items were monotonic (IRT), i.e., item variability is associated with one construct; (4) moderate Spearman correlation (11/17 items); (5) temporal stability - the result of screening did not vary over time. Conclusion: This study shows evidence of validity and reliability of the proposed scale in its intended use of screening for developmental dyslexia. The percentage of children at risk for developmental dyslexia, according to the scale, was approximately 9%, which is in agreement with the international literature on the prevalence of dyslexia.