Hey! So I didn’t really know what to do my blog on this week but as we’ve been doing within and between subjects designs in lectures recently – and I barely understand them myself :p – it seemed appropriate. Enjoy. J
Experimental research designs are used to demonstrate a cause-and-effect relationship between two variables. For this several basic characteristics are required:
- Manipulation on one variable to create set of two/more conditions
- Measurement of second variable to obtain scores within treatment conditions
- Comparison of scores between treatments
- Control of other variables to prevent them becoming a confounding variable
Between subjects designs are also known as independent measures or unrelated measures. Between subjects design is a research design in which each of the different groups of scores are obtained from a separate group of participants.
A between subjects experimental design uses separate groups of individuals for each treatment condition being compared. For example, this design could be used to research the effectiveness of counselling or medication as a treatment for depression by testing the two conditions and determine which participants were less depressed after trials had taken place.
Advantages of a between subjects design:
- Individual score is independent of other scores
- Can be used for a wide variety of research questions/hypothesis – any experiment comparing two/more treatment conditions
Disadvantages of a between subject design:
- Require large number of participants (as each participant gives only one score)
- Individual differences can make the score less valid/reliable
Within subjects designs are also known as a repeated measures design. A within subjects design is a research design in which different groups of scores are obtained from the same groups of participants.
A within subjects experimental design is a design in which the same group of individuals participates in all of the different treatment conditions. For example, a within subjects experimental design can be used to measure reaction times of people.
Advantages of a within subjects design:
- Can use a small sample of participants
- Eliminates problems based on individual differences – can determine variance in data from individual differences
Disadvantages of a within subjects design:
- Each participant goes through series of treatment conditions administered at different times – opportunities for time related factors (e.g. fatigue, illness) to influence participants score
- Participant attrition – some participants may withdraw before study is complete
Gravetter & Forzano (2009) Research Methods for the Behavioural Sciences