Familial patterns of expression of specific reading disability in a population sample

Summary

A sample school population of 75 family units of equal size was investigated for expression of specific reading disability. 25.3% of the total children showed specific reading disability as defined in this study. By using spelling achievement as the criterion for the presence of the disability, the incidence of the disorder was shown to be much higher in certain families than in others, with clear sibling aggregation. The siblings of specific-reading-disability cases demonstrated lower spelling competence than the total siblings in normal families, even when well above a crippling level. Both within individual families and by grades, the spelling rating in relation to grade norms of the specific-reading-disability family cases with their siblings tended to decline with age, in contrast to normal families where it tended to improve with age. This pattern was even more striking if the greater language competence of females, now quite generally accepted and further supported by this study, was taken into account. It was demonstrated that the above patterns were not primarily a product of intelligence level or teaching methods. The bearing of these findings on the tenability of the most common, current hypotheses concerning causation was briefly discussed.