01 NRDC Dyslexia 1-88 update - Texthelp

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Research Report
Thus, if it is a valid observation that ‘standards of clinical practice in the learning disabilities
field have, at various times in its history, reflected more than 50 per cent pseudoscience or
unverified, virtually armchair speculation about human abilities’ (Stanovich, 1999), there can
be scant justification for expecting any consistency in the diagnoses that adult ‘dyslexics’ may
have received as children. The evidence for inconsistency is overwhelming—unsurprisingly,
given the difficulty of operationalising any definition of dyslexia so as to exclude all ordinary
poor readers—and false positives may outnumber true positives severalfold.
Diagnoses of dyslexia are unstable across identification methods.
A diagnosis of dyslexia may be a ticket of eligibility for a particular form of learning
provision rather than a scientific statement.
Are diagnoses of dyslexia stable over time?
In cases where the method of identification is held constant, there is no guarantee that it will
identify the same people as ‘dyslexic’ over time, even though dyslexia is conceptualised as a
lifelong condition. This is particularly likely to be so where identification has been limited to
measures at the behavioural level (Frith, 1999). Several serious problems confront the
researcher or clinician seeking to evaluate adults who report childhood reading and writing
problems: they are often self-selected volunteers, potentially unrepresentative of the
population at large; their elementary school records are not available to document their
school-age reading achievement; diagnostic techniques designed for children may have
norms that are unsuitable for adults; and adults with childhood reading problems might have
adopted compensatory strategies as a result of remedial teaching or self-instruction
(Scarborough, 1984).
So, while the concept of dyslexia assumes that there is a stable group of people who are
underachieving in literacy and whose classification is neither age- nor test-specific, this kind
of stability may not exist (Wright et al., 1996). Some of the apparent change over time may be
attributable to measurement error (Fergusson et al., 1996). As with specific language
impairment (NICHD, 2000), a nonlinear developmental path, with spurts and plateaux, may
lead to unstable perceptions of ‘impairment’ and ‘recovery’. Where the concept of ‘reading
disability’ embraces all poor readers, detailed assessment of ‘recovered’ and ‘non-recovered’
readers has suggested that intelligence, language ability, working memory and the adoption
of a ‘word decoding’ approach to reading and spelling may play a role in ‘recovery’ (Waring et
al., 1996). However, change is not always for the better: in a cohort of children with specific
language impairment, the prevalence of ‘specific reading retardation’ has been found to
increase between the ages of eight-and-a-half and 15 years (Snowling et al., 2000).
Stability of classification is a separate issue within the underachieving group. The question of
subtypes will be examined at greater length in the following section. Meanwhile, it is
sufficient to take note of findings that the characteristics commonly used as a basis for the
classification of developmental dyslexia into ‘phonological’ and ‘surface’ subtypes may reflect
differences in teaching method and strategic choice rather than differences in learning
aptitude (Baron, 1979; Hendriks & Kolk, 1997; Zabell & Everatt, 2002) and that over a twoyear
period, readers have been observed to move from one of these subtypes to the other
(Snowling & Nation, 1997). Proportions in the subtypes may also vary, not only according to
the language in which subjects are assessed but also according to the method used to classify
them and, in a given language, according to the measure used; furthermore, longitudinal data