Experimental Designs (MP, IS, RM)

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What are the design types in experiments?

There are three design types of experiments:

  • Independent Samples
  • Repeated Measures
  • Matched Pairs

Independent Samples is when the sample is divided into different groups. This means that not everyone will experience all conditions in the experiment.

For example, in an experiment that tested the effectiveness of using light treatments for Season Affective Disorder the participants were divided into four different groups and each group used a different type of light treatment for the duration of the study. In studies testing the effectiveness of drugs, an independent samples design would mean that half of the participants would receive the real drug and the other half a placebo (or sometimes there might be a third group that receives no treatment).

Repeated Measures is when the treatment is repeated for all participants. In other words, the participants experience all conditions of the experiment.

For example, if you wanted to test the effects of sleep on memory you might get all your participants to read a passage of words, take a 15 minute nap and then complete a quiz for what they remembered. In a repeated measures design the same participants would also be asked to read a similar passage of words and then take the quiz (with no nap).

Matched Pairs design is quite similar to independent samples in one regard: the sample is divided. Participants are paired up with another participant based on some criteria and then they are separated so they are in a different group from their partner.

In his  bobo doll experiments to see if watching violence can cause children to be violent, Bandura used a matched pairs design by gathering lots of data on the children’s (i.e. participants’) pre-existing aggressive tendencies. They asked their parents and teachers for information and then used a scoring system to rate their aggressiveness. The children were then paired (not physically) with another child who had a similar rating and then put in different groups.

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