Psychology Topic E Studies


Theilgaard (1984): the criminal gene

AIM: To see if criminals had a particular gene that could be responsible for criminality. 

PROCEDURE: Took blood samples from over 30,000 men born in the 1940s and found XXY and XYY abnormalities. 16 had XXY and 12 had XYY. They were interviewed by a social worker about their backgrounds and criminal history and given intelligence tests. A personality test was used to see if they had more aggression than XY males. 

RESULTS: XYY males had slightly lower intelligence levels and were more aggressive (evidence for criminal gene). More similarities between XXY males and XYY males than differences.

CONCLUSION: There is limited evidence that XYY males are more aggressive thsn XY males.

  • STRENGTHS: Tests conducted by independent social worker who didn't know the aim so no bias.
  • Vast range of tests used to measure different aspects of the men's lives, backgrounds and personalities. 
  • WEAKNESSES: Small sample of men, only 12 XYY males tested so results weren't generalisable. 
  • Only shows a correlation, frustration caused by lower intelligence could have made aggression, not the gene.
  • Not all criminals are XYY so we cannot be sure that this abnormality causes criminality at all. 
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Sigall and Ostrove (1975): attractiveness and jury

AIM: Does attractiveness affect jury decision-making? Is there a link between attractiveness and type of crime committed?

PROCEDURE: 120 participants split into 6 different groups of 20 participants were given a card with a crime written on it and a picture of a woman. Each group saw an attractive or unattractive person in a picture (Barbara Helms) or no picture (control group) and read about a fraud or burglary Barbara had committed. They rated how attractive she was and gave a prison sentence from 1-15 years.

RESULTS: Similar sentence length given for both crimes with unattractive and no picture. Attractive picture made them give her a longer sentence for fraud and shorter for burglary.

CONCLUSION: Highlights importance looks can have on a jury, and that good-looking people do get away with some crimes unless they have used their looks to commit a crime. 

  • STRENGTHS: Used good controls (useful control group) with less extraneous variables so reliable findings.
  • Participants less likely to show demand characteristics as they didn't know what other groups were doing.
  • Study could be used in real life.
  • WEAKNESSES: Not realistic as a jury wouldn't experience this and usually only decide if they are guilty or not, not sentences too.
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Madon (2004): self-fulfilling prophecy and drinkin

AIM: To see if a parent's expectation of their child's drinking habits would become a reality.

PROCEDURE: 115 children between 12 and 13 had their parents asked how much alcohol they regularly drank or would drink over the next year. A year later, the children were asked how much they actually drank.

RESULTS: Children who drank the most had parents who predicted a greater use of alcohol and the child seemed at greater risk of higher alcohol use if parents held negative beliefs about their child's drinking habits.

CONCLUSION: Parent's prediction usually accurate and consistent. Could be self-fulfilling prophecy, as what they expected came true. Study could show that a parent's beliefs has a massive influence on child's behaviour. 

  • STRENGTHS: Large sample of participants so results are more likely to be valid.
  • Gives a strong warning to parents about holding negative beliefs about their children - they could become true.
  • WEAKNESSES: Parent's could have just been accurate and not have influence their children. 
  • Other influences could have occured, such as friends influencing the children.
  • Study only shows a correlation and researchers cannot be sure of a true link between the variables. 
  • The questionnaire could have social desirability bias. Children could say they drink more to look tough, or drink less in case their parents find out. Parents could predict they drink more as a badge of honour, or less as they think it is not acceptable. 
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