Bowlby's natural experiment
1. Analysed case histories of 88 patients in the Child Guidance Clinic in London
2. 44 children had been accused of stealing (the '44 thieves')
3. Other 44 formed a control group of non-criminals but emotionally disturbed young people
4. Bowlby found that 14 (32%) of the 44 thieves could be described as affectionless psychopaths
5. Of the 14 affectionless psychopaths, 12 (86%) had experienced prolonged separation from their mothers in the first two years of their lives