01 NRDC Dyslexia 1-88 update - Texthelp

Developmental dyslexia in adults: a research review 39
Dyslexia subtypes do not occur naturally; they are artefacts of research and teaching
strategies.
Is there any bias in our perception of dyslexia?
In literacy practices there are cross-cultural differences. Some, like differences between
English and Chinese writing and spelling systems, are obvious (Gleitman & Rozin, 1977);
others, like differences between English and Chinese readers in brain morphology and
function, are not (Hsieh et al., 2001). In dyslexia, too, there are cross-cultural differences
reflecting differences between writing and spelling systems (Habib et al., 2000; Paulesu et al.,
2001); there are also cross-cultural similarities (Ho et al., 2000; McBride-Chang & Kail, 2002).
In passing, it deserves mention that not even the Chinese are ‘Chinese’ (as opposed to
‘Phonecian’) readers, since Chinese characters contain not only semantic but also phonetic
elements (McBride-Chang & Ho, 2000). However, dyslexia is more evident in alphabetic
writing systems than it is in nonalphabetic systems, like Chinese. It is also more evident in a
morphophonemic spelling system with complex relationships between phonemes and
graphemes, like English, than it is in a phonemic system with simple relationships between
phonemes and graphemes, like Finnish. In these respects, there is cultural bias.
Writing systems are not the only potential sources of cultural bias in dyslexia. Differences in
socio-economic status—the standard proxy measure of differences in educational and social
opportunity—have long been implicated in the debate about dyslexia. Here, there is a paradox.
Some parents may believe that exceptional abilities in music or mathematics are ‘innate’
when their children have no obvious flair for them, but if their children are found to be
deficient in a skill such as reading they will blame environmental influences such as poor
teaching (Bateson & Martin, 1999). Other parents accept personal responsibility even while
denying it, as they embrace the social cachet of dyslexia (which might be heritable) while
disclaiming the social stigma of low intelligence (which is also heritable). A clinical
psychiatrist has observed that when mothers are asked what makes their children tick, they
‘plump for whichever nature or nurture theories most conveniently let them off the hook—
largely, of course, to avoid guilt’ (Oliver James, in The Guardian, 25 September 2002, G2, page
8).
It is probable that there is a white-collar or class bias in reporting dyslexia; it would be very
surprising if there were not. However, reporting bias could be expected in clinic (or special
school) samples, but not in community (epidemiological) samples, because epidemiological
sampling is less likely to be affected by the economic and social factors that bias clinic
referral and special school enrolment. A systematic study has investigated this question in a
community sample, avoiding the use of an IQ-discrepancy formula. It found that the
prevalence of dyslexia—and ‘any attempt to determine the prevalence of dyslexia should be
treated with caution’ (Miles & Miles, 1999)—varied only at the extremes of the social scale
(Miles et al., 1994). Because of the uneven distribution of IQ scores across the social
spectrum (Mackintosh, 1998; Neisser et al., 1996; Sternberg, 2000), a prevalence estimate
based on an IQ-discrepancy operationalisation of the dyslexia concept would necessarily be
higher for middle-class than for working-class groups (e.g. Wadsworth et al., 2000) and this
would reflect identification bias but not cultural bias. Nevertheless, it may be that the literacy
difficulties in most children, even those from middle-class backgrounds, are caused by
experiential and instructional deficits, not by basic deficits in cognitive abilities (Vellutino et
al., 1996).