1. Experimental Design

2. Recap
What are IVs and DVs?

3. Conditions In an experiment you can have two conditions
The experimental condition is where you manipulate a variable to see the effect
The control condition is where nothing is manipulated so that we have a base line to compare our results with.

4. Conditions Identify the conditions:
An experimenter wants to see if drug X improves sport performance. One group are given the drug, another are given a placebo. Both groups are tested for athletic ability.
Note that not all experiments will have a control condition (when testing for a difference between men and women for example)

5. Task On the handout Identify the IV and the DV
Identify the two or more conditions in the experiment, highlighting which condition is the control (if there is one)

6. What do we mean?
Experimental design refers to how we use our participants in our experiment
There are three main ways that participants can be used.
Independent measures
Repeated measures
Matched pairs

7. Repeated measures
In repeated measures, each participants takes part in every condition
E.g. to test the effect of caffeine on mood, participants have their mood assessed, drink a cup of coffee, then have their mood assessed again.
Control condition: no caffeine
Experimental condition: caffeine =

8. Repeated Measures Strengths Weaknesses No participant variables
Fewer participants are needed
Weaknesses
Risk of demand characteristics
Risk of order effects; boredom, fatigue and practice effects

9. ≠ Independent Measures
In an independent measures design, each participant is only used in one condition
E.g. to test the effect of caffeine on mood, one group of participants are given coffee, another group are not. Both groups have their mood assessed before and after
Control condition: no caffeine
Experimental condition: caffeine ≠

10. Independent measures Strengths Weaknesses
lower risk of demand characteristics
No order effects such as boredom, fatigue, or practice effects
Weaknesses
Higher risk of participant variables
More participants are needed

11. Matched pairs
Matched pairs is similar to repeated measures, but the participants in the groups are matched with each other, so that the two groups are as similar as possible.
E.g. before a study, the experimenter selects two groups of participants, and matches them on age, gender and intelligence. One group of participants are given coffee, another group are not.
Control condition: no caffeine
Experimental condition: caffeine ≠

12. Matched pairs Strengths Weaknesses Participant variables are reduced
No order effects
Less risk of demand characteristics
Weaknesses
Participants can never be completely matched
Time consuming and expensive
More participants required

13. Experimental designs activity
I am testing the effect of music on concentration. In my experimental condition I will play loud music and get the participants to answer general knowledge questions. In my control condition I will give a general knowledge test without music

14. Experimental designs activity
Stand up! You are my participants.
Organise yourself into
Independent measures
Repeated measures
Matched pairs

15. Task
Identify the experimental design used in the examples