Natural Experiment

Natural Experiment

1. Quasi-Experiments

   • Unlike lab and field experiments the experimenter in a quasi or semi-experiment does not manipulate the IV.
   • The IV is usually already in place and the experimenter just measures the DV.

2. Hodges and Tizard (1989)

   • Method
     • Longitudinal natural experiment comparing children in an institution with those raised at home.
   • Sample
     • 65 children who had been placed in a UK institution when they were 4 months old.
   • The staff in the institution gave children lots of attention, but there was a policy of not forming attachments with children in their care.
   • There was a high turnover of staff. Before the age of four, children had up to 50 different caregivers.
   • By 8 years, 24 had been adopted, 15 had returned to their homes and 26 remained in the institution.
   • Children were assessed at 4, 8 and 16 and were compared with a control group of "normal peers" raised at home.
   • Results
     • By age 8, adopted children were as attached as the control group.
     • This was not true of children who returned to their natural families.
     • Restored children may have returned to the same environment that prompted the difficult behaviour, whereas the adopted children went to families who really wanted a child.
   • However...
     • Compared with the control group, both adopted and restored children:
       • South adult affection and attention,
       • were less successful in social relationships,
       • had more difficulties at school,
       • were friendly to all peers rather than having a special friend.
   • Conclusion
     • Adopted children had better relationships than restored children.
     • But all displayed behavioural problems compared to attached children in the control group.
   • Evaluation
     • 1) An experiment requires that subjects are allocated randomly to two groups
       • Children may have been allocated to the adopted or restored group based on their characteristics
         • e.g. were adopted children more sociable?
     • 2) Only 42 of the 65 were followed to the end.
       • The drop outs may have biased the sample.

3. Quasi - Experiment

   • Advantages
     • High ecological validity
     • Little or no sampling bias
     • Demand characteristics minimised
   • Disadvantages
     • No control over IV
     • No control over extraneous variables
     • Impossible to replicate unless it occurs again naturally
     • Ethics - consent, privacy, deception