01 NRDC Dyslexia 1-88 update - Texthelp

Developmental dyslexia in adults: a research review 23
Researchers use at least eight different methods to identify people with dyslexia.
Their choice of method determines which people will be identified as dyslexic.
A participant who is dyslexic in one research study would not necessarily be dyslexic in
another.
3. Choosing the comparison group
Just as the identification of target groups is problematic, so is the identification of their
normal comparisons:
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A researcher may choose to compare dyslexic people and superior readers of the same age
(the ‘age-level’ match).
To compare dyslexic people with a younger but normally-reading group (the ‘reading-level’
match). Implicit (if not explicit) in these comparisons are two assumptions: that all poor
readers are dyslexic and that all dyslexics are poor readers.
A third strategy is to take an undifferentiated group of people with low reading skills and
subject their test scores to factor analysis or a similar technique in order to identify subgroups
of dyslexic and non-dyslexic people. This strategy is essential for investigating claims
that dyslexic people can be distinguished from ‘ordinary poor readers’.
A fourth strategy, albeit an uncommon one, is to compare discrepancy-defined dyslexic
people with non-discrepant, age-matched ‘ordinary poor readers’.
Where reading-level matches are involved, there is a choice of measures, some of which
might be more appropriate than others. For example, word recognition skills might provide a
more appropriate match than reading comprehension level does; the two measures may
identify different although overlapping target groups. In word recognition, a measure of
decoding accuracy for regular words or pseudowords might conceivably identify a different
comparison group from that identified by measures of irregular-word reading or reading rate.
Given that readers make strategy choices or trade-offs between speed and accuracy, the
composition of these groups might—and probably will—change over time.
Where researchers attempt to match groups on IQ, they have a choice between full-scale,
non-verbal, or verbal measures and this choice, too, will influence the selection of
comparison group members. If no attempt is made to match the groups on demographic
measures, they may nevertheless be found to differ in terms of socio-economic status and all
that this difference implies with respect to language development and educational
opportunity.
Whether and how dyslexic people differ from non-dyslexic people depends on the
researcher’s choice of comparison group.
Researchers have at least four options for choosing comparison groups.
Within those options, there are further sources of variation.