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Abstract
Does the choice of test for assessing reading comprehension influence the outcome of genetic analyses? A twin design compared two types of reading comprehension tests classified as primarily associated with word decoding (RC-D) or listening comprehension (RC-LC). For both types of tests, the overall genetic influence is high and nearly identical. However, the tests differed significantly in how they covary with the genes associated with decoding and listening comprehension. Although Cholesky decomposition showed that both types of comprehension tests shared significant genetic influence with both decoding and listening comprehension, RC-D tests shared most genetic variance with decoding, and RC-LC tests shared most with listening comprehension. Thus, different tests used to measure the same construct may manifest very different patterns of genetic covariation. These results suggest that the apparent discrepancies among the findings of previous twin studies of reading comprehension could be due at least in part to test differences.
ACKNOWLEDGMENTS
Initial work on this manuscript was done when R. Betjemann was at the Institute for Behavioral Genetics at the University of Colorado as a Postdoctoral trainee on NIMH training grant T32 MH016880-25. This research was also supported by a grant from NIH HD27802 to the Colorado Learning Disabilities Research Center. Preliminary analyses of these data were presented by J. Keenan at the Reading Comprehension: Theory to Practice workshop, April 2007, Oxford, UK, and at The 1st Stavanger Reading and Writing Conference, September 2007, Stavanger, Norway, and the final analyses were presented at the Pacific Coast Research Conference, February 2009. We are grateful to all the participants and their families, and to all the testers and scorers.
Notes
1This current sample overlaps with the samples used in some previous studies referenced in this article. Fifty participants in this sample (7.8%) were in the CitationBetjemann et al. (2008) sample, 354 (55%) were in the CitationKeenan et al. (2006) sample, and 422 (65%) were in the CitationKeenan at al. (2008) sample.