Jacob’s XYY

• XYY Syndrome:

  Strengths:

  • Jacob et al found an association between XYY syndrome and offenders imprisoned for violent behaviour.
  • Price and Whatmore found some links between the syndrome and property crime.
• XYY Syndrome:

  Limitations:

  • Even if some violent offenders have the syndrome, this doesn’t prove it is the cause of their violence.
  • XYY males are tall and well-built, so they fit the stereotype of ‘violent offenders’ and get labelled as such by the courts, so huge are more likely to get a prison sentence. As a result, XYY males are over-represented in samples drawn from prisoners And this overstates the importance of the syndrome as a possible cause of crime.
• XYY Syndrome:

  Limitations (2):

  • Alternatively, XYY males may be over-represented in prison because they often have low intelligence, meaning they are more likely to be caught. Samples drawn from prisoners are therefore skewed.
  • The syndrome is very rare (only about 1 in 1000 men have it), so it cannot explain much crime.