Conclusions on the validity of LADS Plus
The process of developing LADS and LADS Plus has involved three detailed studies of the validation of the dyslexia-sensitive tests, first in their full form, and then in their adaptive forms, including verification of the accuracy of the adaptive fractionation algorithm devised for the program, and checking for gender bias. Participants from several different institutions have been involved. In addition, the reasoning modules have been adapted from similar tests in an established and already widely used test suite, which has been independently validated. The development of LADS Plus conforms to the requirements of the British Psychological Society’s Guidelines for the Development and Use of Computer-Based Assessments (BPS, 2002).
Subsequently studies, including the BDA project at Wetherby YOI during 2004-05 enabled further refinement of the program. Thus it may be safely concluded that LADS Plus meets established psychometric criteria for validity and can therefore be used with confidence as a screening test for dyslexia. The individual tests in LADS Plus have good accuracy to discriminate between dyslexic and non-dyslexic adults and are free of gender bias. Furthermore, the combination of the three LADS Plus scores, either as a composite score, or as a qualitative profile, or both, provides a very high degree of accuracy — much greater than reliance on the individual test results alone. However, it should not be forgotten than LADS Plus is a screening test and, as such, is inevitably subject to some degree of classification inaccuracy. The tests in LADS Plus assess core the cognitive skills that are typically weak in dyslexia (phonological processing, lexical access and working memory) and so would be expected to detect the majority of adults with dyslexia. However, adults with atypical forms of dyslexia (e.g. cases in which phonological processing deficits are not found or where visual processing deficits predominate) would not be detected by LADS Plus. The careful development and validation process that LADS Plus has been subjected to has sought to minimise of classification inaccuracy as far as has been practically possible, given the brevity of the tests in the program. In order to keep errors to a minimum, Administrators should refer to Chapter 4 when interpreting results and making decisions about adults who have been screened using LADS Plus.