Bowlby's maternal deprivation hypothesis.
According to Bowlby; 'breaking the maternal bond with the child during early years of life is likely to have serious effects on it's intellectual, social and emotional development'. These effects are permanent and irreversible.
His 44 thieves study supports this, seeing if there was a link between early separation and affectionless psychopathy. He used 44 children who were reffered for stealing, they were compared to 44 children that had emotional issues but had not stolen. He found that 32% were affectionless psychopaths, with 86% of those diagnosed as this having had a separation lasting at least a week before the age of 5. Only 17% of thieves without A.F had been maternally deprived.
The conclusion was that there was a definite LINK between affectionless psychopathy and early separation. In other words, a lack of continuous care may lead to emotional maladjustment.
Evaluation of 44 thieves and maternal deprivation
There was a tiny sample and this means it is difficult to generalise outside of the sample as it may not account for everyone, with not 100% link being found, this is more of an issue.
This did however, show that there is a link between separation and emotional development, thus supporting the theory.
It lacked internal validity, being an observation, he had no control and therefore reliability is weak.
Douglas supported the theory, stating that those that had repeated admissions to hospital were likely to have behavioural issues later in life.
There could be experimenter expectancy bias as Bowlby may have acted subjectively when interviewing the participants, they could have also lied about their deprivation, it may be difficult to tell something from such a long time ago.