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© Banff and Buchan College 2004 Explanations of Phobia Biological –Genetics –Nervous system abnormalities Psychological –Learning theory
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© 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
© Banff and Buchan College 2004
Explanations of Phobia• Biological
– Genetics– Nervous system abnormalities
• Psychological– Learning theory
© Banff and Buchan College 2004
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
© Banff and Buchan College 2004
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
© Banff and Buchan College 2004
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
© Banff and Buchan College 2004
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)
© Banff and Buchan College 2004
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