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Experimental Design. Recap  What are IVs and DVs?

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Presentation on theme: "Experimental Design. Recap  What are IVs and DVs?"— Presentation transcript:

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 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 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 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 


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