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

2. Evidence from family studies
There is now evidence that there is a relationship between the biological relationship and the risk of developing schizophrenia.
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%.

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

4. Evaluation x Family studies are often inconclusive.
x There may be other factors/ approaches that can cause individual's behaviour, such as poor socialisation/ family problems. For cognitive approach, individual’s thought processes may not be rational.
It is a longitudinal study- so it can provide more reliable data, however because the study has collected data over many years the data can be out- dated.