© Banff and Buchan College 2004 Phobias. © Banff and Buchan College 2004 Phobia Main symptoms:...

© Banff and Buchan College 2004

Phobias

© Banff and Buchan College 2004

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

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Explanations of Phobia• Biological

– Genetics– Nervous system abnormalities

• Psychological– Learning theory

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Genetic Influences• Compare concordances of MZ & DZ twins

Same genes Same environment

MZ twins

DZ twins

• Greater similarity of MZ twins is assumed to indicate a genetic influence

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Genetic Data (Simple Phobia)MZ DZ

Carey & Gottesman (1981) 13.0 8.0

Kendler et al (1992) 25.9 11.0

Kendler et al (2001) 15.9 7.7

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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

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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)

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