1. Phobia Main symptoms: –Marked and persistent fear –Anxiety response –Avoidance –Interferes with everyday activities –Duration 6 months or more Affects 6-11% of population (more F) Lifetime problem in 10% of cases www.psychlotron.org.uk

2. Explanations of Phobia Biological –Genetics –Nervous system abnormalities Psychological –Learning theory www.psychlotron.org.uk

3. Genetic Influences Compare concordances of MZ & DZ twins Same genesSame environment MZ twins DZ twins  Greater similarity of MZ twins is assumed to indicate a genetic influence www.psychlotron.org.uk

4. Genetic Data (Simple Phobia) MZDZ Carey & Gottesman (1981)13.08.0 Kendler et al (1992)25.911.0 Kendler et al (2001)15.97.7 www.psychlotron.org.uk

5. Genetic Data (Simple Phobia) MZ concordance usually significantly higher than DZ –Suggests genetic influence MZ concordance always significantly lower than 100 –Indicates environmental influence is also in operation www.psychlotron.org.uk

6. Twin Studies Commonly affected by several problems: –Small samples (NB: not always – check) –Unreliable zygosity tests (early studies only) –MZ twins tend to be treated more similarly than DZ, which may account for greater similarity –DZ twins can be M&F, which may be important with sex-differentiated disorders (like simple phobia) www.psychlotron.org.uk