• If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • Stop wasting time looking for files and revisions. Connect your Gmail, DriveDropbox, and Slack accounts and in less than 2 minutes, Dokkio will automatically organize all your file attachments. Learn more and claim your free account.



Page history last edited by PBworks 13 years, 11 months ago

Key Study


Holland et al (1988)


A study of Anorexia Nervosa twins



The aim of the study was to investigate if there was a genetic basis to AN. If there was a higher concordance rate in identical twins than non-identical twins this would be evidence for a genetic explanation.



The procedure of the study was to compare the incidence of a diagnosis of AN in identical (monozygotic or MZ) and non-identical (dizygotic or DZ) twins. All the twins had been reared together (i.e. shared similar environments). They were assessed by questionnaires and physical measures.



The findings were that there was a 56% concordance rate among the MZ twins but only 5% among the DZ twins. The difference was highly significant.



The researchers concluded that there was a large genetic component in AN and estimated this statistically to be about 80%. However the fact that the concordance was not 100% in MZ twins (remember these have identical genes) indicates that the environment still has a role to play.




However all twin studies have criticisms. For one thing, it could be argued that MZ twins have a more similar environment than DZ twins (e.g. they are often dressed and treated the same way). This could account for their greater similarity in terms of vulnerability to disorders like AN. Also twin studies are based on very small samples – only 25 MZ and 20 DZ twins. This can make it difficult to generalise from the results.


Back to Biological Explanations


Back to Summary of Key Studies



Comments (0)

You don't have permission to comment on this page.