1. Experimental Designs You have to carry out an experiment to discover if watching horror films gives children nightmares. You have 5 minutes to decide how you might carry this out in order to briefly report back to the class

2. Independent P’s Design Each p acts in one condition only, so p’s in each group are entirely different. Example: Testing IQ differences between males & females Condition 1Condition 2 John Laura John Laura Simon Jane Simon Jane Jack Beth Jack Beth Brad Sara Brad Sara

3. Advantages: 1. P’s are unlikely to guess aim of study (why?) 2. It is not too time-consuming for p’s (why?) 3. We can use the same IQ test in each condition which saves time. 3. There are no practice or boredom effects (ORDER effects).

4. Disadvantages: 1. Will need more p’s than for a repeated design where each p is in both conditions. 2. P’s all have individual differences so group 1 may behave differently to group 2 simply because they are different people with different personalities & traits (not just because of gender in this case).

5. Repeated Design Each p takes part in both or all conditions of an experiment, so they REPEAT the procedure. Example: Testing effects of noise on ability to complete a task. Noise conditionSilence condition JulieJulie PaulPaul SallySally JakeJake

6. Advantages 1. Individual differences between p’s are not an issue. Why? 2. Only half the number of p’s are needed compared to an independent design.

7. Disadvantages 1. It is time-consuming for p’s to repeat the procedure. 2. P’s may guess the purpose of the study and change their behaviour to please the experimenter (or mess up the study). 3. May get ORDER EFFECTS. P’s may get better due to practice or worse due to boredom.

8. Matched Design P’s are matched in pairs (sometimes after a pre-test). One of each pair is put into the experimental condition and one in the control. Example: Testing effects of violent TV on children’s behaviour. Experimental ConditionControl condition DanSam MollyPolly BillBen HarryLarry

9. Who would be the most ideally matched pairs? P’s are matched on what might be seen as appropriate criteria, such as age, gender, IQ, size, skill level, etc.

10. Advantages 1. There are no order effects with this design. Why? 2. P’s are not likely to guess the aim of the study. Why? 3. It is not time-consuming for p’s. Why? 4. Individual differences are reduced (but not entirely eliminated – Why?)

11. Disadvantages 1. It is very difficult to find pairs of identical twins. 2. It is time-consuming for the E and the P’s to carry out pre-tests or go through a matching exercise. 3. Participant variables are never totally eliminated.