Key study: Holland et al (1988) Aim: – To examine if there is a higher concordance rate between MZ twins than DZ twins for AN – MZ twins share 100% of genes, DZ twins 50% – If AN was genetic, there should be a higher rate amongst MZ twins

Key study: Holland et al (1988) Procedure – Opportunity sample of 34 pairs of twins based on one of the pair having a diagnosis of AN – Natural experiment (IV is naturally occurring: genetic similarity) – Longitudinal study – Interview + typical diagnosis for AN

Key study: Holland et al (1988) Findings – Significant difference between MZ (56% concordance) and DZ (7% concordance) twins – Also, other psychiatric illnesses were common amongst non-anorexic twins

Key study: Holland et al (1988) Conclusions – Suggests that AN may have a genetic influence – The fact that the concordance was not 100% shows that genes are not completely responsible, they just provide susceptibility to the disorder – This suggest that other influences are crucial

Key study: Holland et al (1988) Criticisms – The high concordance may be due to factors other than genes – MZ twins tend to share a more similar environment than DZ twins The look and behave similarly and are therefore treated alike – No control of IV (natural experiment) therefore this does not control for the fact that other variables may be involved – Ethnocentric (culturally biased – western only)

Key Study Behar et al (2001) Study of psychological explanations of eating disorders

Behar et al (2001) Aims – Effect of gender identity on eating disorders (ED) – Do behavioural explanations of eating disorders have any evidence? – Women may feel more pressure to be thin than men (idealised body image) – Is acceptance of the feminine gender role higher in ED women than normal controls?

Behar et al (2001) Procedure – 126 participants (63 ED + 63 controls) – Natural experiment (ED not controlled by experimenter) – Clinical interview to ensure ED – Questionnaire to measure gender identity (BEM sex-role inventory)

Behar et al (2001) Findings – Significant differences in gender identity in ED and non-ED – More ED were classified as feminine gender identity (43% compared to 23.8% controls) – More controls were found to be androgynous (31% compared to 19% ED) – More controls were undifferentiated (43% compared to 27%)

Behar et al (2001) Conclusions – Supports SLT view that ED may be due to pressures women face in society to look a certain way – Shows the positive aspects of androgyny

Behar et al (2001) Criticisms – Ignores genetic, cognitive and conditioning factors – Not a true experiment (no control over IV) – causation cannot be directly attributed to the IV. In this case, it could mean that ED caused the change in gender role identity – Ethnocentric