Brengden (twin & contemporary study)

• What was Brengdens aim?

  > To see the extent to which social and physical aggression are explained by genetic and environmental influences

  > To see if one type of aggression leads to another type
• What is social aggression?

  > Social status are used to damage reputations, manipulate and inflict (e.g. spreading rumours)
• What is physical aggression?

  > Threatens physical harm (e.g. getting into fights)
• What was Brengdens sample?

  > 6 year old children

  > Used secondary data as part of a longitudinal study (Quebec Newborn Twin study)

  > 234 twin pairs - 44 Mz male + 50 Mz female, 41 Dz male + 67 Dz mixed
• How did Brengden approach ethical guidelines?

  > Written consent from parents

  > Approved by the institutional review board
• How did Brengden collect teacher data?

  > Sociometric data

  > Rated each child's social and physical aggression using statements

  > Responses were given on a 3 point scale

  > Responses added to a total social aggression score and a total physical aggression score
• How did Brengden collect peer data?

  > Each child was given a booklet containing photos of every child in the class

  > Circled 3 pictures of children they thought matched the behaviours (e.g. gets into fights)

  > Recieved a total social aggression score and a physical aggression score
• How was this data analysed?

  Mz ratings were compared with sae sex Dz ratings
• What were Brengdens results?

  > Mz twins were twice as high as Dz for physical aggression

  > Mz twins and Dz twins for social aggression were similar
• What did Brengden conclude?

  > Social aggression was due to genetic factors

  > Physical aggression was due to environmental factors

  > Physical aggression can lead to social aggression but social aggression cannot lead to physical aggression - Social aggression is more socially acceptable so people don't need to be physically aggressive