April 26, 2008
The biological model attributes abnormality to four causes; genetics, damage to the brain, viral infection, and chemical imbalance. The Holland et al study concluded that MZ twins have a 56% risk of anorexia if one twin already has it, compared to a 1-4% risk in the rest of the population. Despite the obvious correlation, other factors than genetics must play a part in mental abnormality, or there would be a 100% concordance rate. Besides, the sample size was far too small, so we cannot generalise the findings. A sample of 15,000 twins would be required to establish cause and effect.