Are twins delayed in language development?

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Are twins delayed in language development?

I have located an excellent review of the published literature on this subject (Jennifer Ganger).

Contents:

I. Introduction

II. The Early Years

A. Classics
B. Case studies
III. Progress

A. Some often-cited studies
B. Random
C. Examination of the biological factors
D. Non-biological variables

IV. Commentary and Further Reading

V. References

I. Introduction
There is a pervasive assumption in the twin and language development literature that twins are somewhat delayed in language development and more prone to language disabilities.

What I want to present here is a review of conclusions from some papers I looked through when I was trying to settle the issue of whether studies on language development in twins are "generalizable" to the non-twin population. That is, whether or not twins are significantly different from the non-twin population with respect to language.

To preview the conclusion, the consensus in the literature seems to be that being a twin does in fact make a child more prone to language delays and disorders due to several biological and social factors. As we shall see, though, any of these factors can also affect singletons; twins are often just more prone to them. Furthermore, most studies show twins catching up to their singleton peers on standardized language tests during early childhood. The conclusion, then, is that twins should not be considered a special population that is differentially at risk for the mere fact of being a twin.

Contents

II. The early years
A. Classics

The pervasive assumption of the inferiority of twins in language originates with two papers from the 1930's which remain two of the largest studies to date of the language of twins as a group. These are Day (1932) and Davis (1937).

Day studied 80 pairs of twins and 140 singletons. The children were aged 1.5 to 5.5. There were 20 pairs of twins at each of 2, 3, 4, and 5 years of age. 50 spontaneous utterances were recorded from each child while playing with experimenter's toys. On several gross measures of language complexity (such as sentence length, number of different grammatical categories in a sentence) twins were found to be as much as two years behind singletons by the age of five.

Davis carried the same methodology to twins aged 5-9 and found that on structural measures the twins caught up with singetons on average, but were still more likely to have articulation problems.

However, there are several flaws in these studies (I am not the first to point them out). First, no effort was made to exclude twins who had language, speech, or hearing pathology. Since these are more common in twins (probably for reasons I'll mention below), it is possible some of these subjects were included in the sample and lowered the overall results correspondingly. Second, no information was reported on birth weight or time of gestation of the twins, both of which may be factors in language delay. Third, birth order was not considered as a possible factor, and later birth order is also known to be associated with ...