Kendler et al (2006)

• Kendler et al 2006

  Aim - determine heritability of MDD in a large swedish sample
• Kendler et al 2006

  Participants - Over 15000 complete twin pairs registered in the national Swedish Twin Registry
• Kendler et al 2006

  Procedure - They carried out telephone interviews over a period of 4 years to diagnose lifetime MDD on the basis of the DSM-IV symptoms or having had a prescription for antidepressants. The twins were also asked about their shared or individual specific environment that may have made a twin more susceptible to depression
• Kendler et al 2006

  Results - The average concordance rate for MDD across the twins was 38%. There was no correlation between number of years twins had lived together and MDD, suggesting it was a true heritability rate. The rate among female MZ twins was higher than among male MZ twins. Rates for dizygotic twins were lower overall. The difference between MZ and DZ concordance rates is enough to indicate a strong genetic component
• Kendler et all 2006 was correlational so no cause and effect. There was no particular gene isolated, but it did confirm previous research about reliability. Information about life events and MDD symptoms were self reported. Diagnosis by telephone may be of questionable validity. Large sample size mediates some of the concerns above though