Holland et al (1984)
Holland et al set out to find a genetic link in those who suffered from anorexia nervosa by using twins. Twins, a natural and perfectly normal occurrence, are an extremely good means to research genetic links in any sort of psychological experiment. This is because of the genes the two siblings share. Monozygotic twins (MZ) share 100% of the same genes. Their physical appearances are often identical, though Dizygotic (DZ) twins, who share 50% of the same genes, can also appear identical too (in rare cases). If there was any uncertainty with a pair of twins, Holland et al carried out a blood test.
The sample of twins (where at least one of the twins in each pair suffered from anorexia) was thirty female twins (16 MZ and 14 DZ pairs), four male twin pairs and one set of male triplets.
The findings on this case were that there was a higher concordance rate in monozygotic female twins (55%) in comparison to the 7% of dizygotic female twins. Although approximately nine of the female co-twins did not suffer from any sort of disorder, it was found that five of the non-anorexic female co-twins suffered from either other psychiatric illnesses or minor eating disorders.
In terms of the male twins (or triplets) none of them had anorexia and was therefore, discordant, though an interesting find was that the anorexic male of the twins appeared to have been disadvantaged at birth and to be the less dominant of the pairs.
The conclusion appeared to be in favour of a genetic link to developing anorexia, considering the high concordance rate in twins with 100% of the same genes.
Many criticisms can be made from this experiment. For one, the experiment did not seem to take into account the amount of environmental influence which could have affected the results. For example, in more cases and not, it is found that monozygotic twins are treated more similarly than dizygotic twins. This could mean that they are exposed to the same pressure, influences and experience as each other, and would mean that if one developed anorexia through environmental stimulus, then the other would be more likely to develop it too. Dizygotic pairs, though still twins, are less likely to be treated similar due to the (often) distinctive appearances of the two individuals. Albeit growing up in similar environments, the two may be exposed to different and separate influences and is therefore less likely to develop anorexia if the other twin has it.
Another criticism is of the lack of personal information given by the subjects. Though privacy should be provided, it is valuable to have information such as age and ethnicity as part of this experiment. It is said that approximately 1% of schoolgirls and university students suffer from anorexia in the UK alone, and so the high concordance rate of the monozygotic twins could be explained by perhaps the majority of the monozygotic twins belonging to this age range, therefore, the likelihood of the findings would be more in favour to higher concordance. Likewise, the lower concordance rate in the dizygotic twins could be explained by there being less pairs coming from this age range. Ethnicity is also a slight factor in the probability of contracting the illness. It was shown that the rates of anorexia is most prevalent in Caucasian women. The effects of this information is similar to age, where if the pairs of twins were mostly of Caucasian ethnicity, the percentage of higher concordance would most likely be more prominent than if they were of mixed ethnicities.