The study of twins / Peter Mittler.

  • Mittler, Peter J.
Date:
[1971]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The study of twins / Peter Mittler. Source: Wellcome Collection.

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    82 Cognitive Processes (1937), Burt (1966) has argued that his own sample of fifty- three separated identical pairs were not selectively placed in foster homes comparable to those of the natural parents; in fact, his figures suggest that a disproportionately large number of placements occurs into working class families. Burt's study deliberately excluded twins who were brought up by other members of the family. The number of separated identical pairs investigated by psychologists now amounts to about 100, but Burt is of the opinion that many more could be found if a more diligent search of local authority records were carried out by edu¬ cational psychologists and others with access to children's departments' files. Larger numbers need to be studied be¬ cause of the risk of social bias in the samples. We need to be sure that families who consent to their twins being separated do not represent an undue proportion of im¬ poverished or 'problem' families who simply could not afford to look after two more infants. Examination of Burt's figures (1966) suggests that a disproportionate number of separated twins come from the lowest two occupational categories (thirty-two out of forty-seven, and another six in institu¬ tions); there may therefore be more substance than he admits in the criticism that because his separated twins do not come from 'the full range of the social and cultural scale', 'environmental differences have not had a fair oppor¬ tunity to reveal themselves' (Halsey, 1959, cited by Burt, 1966). Burt argues that only a small number of the children were in private schools, but the skewed social distribution of his sample remains; on the other hand, the variance of his sample on IQ tests is comparable to that of the general population. Another means of checking the effect of separation is to compare those separated within the first six months with those who were only separated after a year or more spent in the same environment. This was done by Vandenberg and Johnson (1968) who re-analysed data from all eight studies of separated pairs, including the original nineteen pairs studied by Newman. They report larger IQ differences for