Outline what is meant by independent groups and repeated measures.

Discuss the strengths and weaknesses of both of these types of experimental design.

**Outline:** An independent groups design is where different participants are used in each condition of the experiment. Participants are usually randomly allocated to one group or the other. A repeated measures design is where the same participants take part in all conditions of the experiment. Each participant experiences both the experimental and control conditions. **Discussion:** **Independent Groups:** A key strength of the independent groups design is that there are no order effects. Since participants only take part in one condition, their performance cannot be affected by practice, fatigue, or boredom from having done a previous condition. A major weakness, however, is the potential for participant variables. The different groups may contain people with different characteristics (e.g., one group might be more intelligent or motivated by chance), which could affect the results. This can be partly controlled by random allocation. **Repeated Measures:** A key strength of the repeated measures design is that participant variables are controlled. Since the same people are in both conditions, any differences in results are more likely to be due to the independent variable, not individual differences between participants. This means fewer participants are needed overall. However, a major weakness is the risk of order effects. Participants may perform better in the second condition due to practice (a practice effect) or worse due to tiredness (a fatigue effect). This can be dealt with by using counterbalancing, where half the participants do condition A then B, and the other half do B then A.