1. Kendler et al (1985) Kendler et al (1985) Genetic explanation of schizophrenia

2. Evidence from family studies First-degree relatives (parents, siblings and offspring) share a average 50% of their genes and second- degree relatives share approximately 25% of genes. The rate of schizophrenia in the general population is about 1%. Studies compare rates of schizophrenia in relatives of diagnosed cases compared to relatives of controls. There is now evidence that there is a relationship between the biological relationship and the risk of developing schizophrenia.

3. Kendler et al (1985) Family studies report that first degree relatives of schizophrenia patients have a higher prevalence of personality disorders, e.g. schizophrenia/ paranoia. Shown that first- degree relatives of those who have schizophrenia are 18 more at risk than general population. Therefore suggesting that there may be a spectrum of disorders genetically related to schizophrenia.

4. Criticisms Family studies are often inconclusive- because they are conducted retrospectively. They are comparing a cross section of people who have already been diagnosed. It is a longitudinal study- can provide more reliable data and a number of large- scale projects have been undertaken in different parts of the world. There may be environmental influences for individual's behaviour.