What is a hypothesis?
Before a psychologist sets out to do an experiment he will normally have formulated a hypothesis. This is a statement the psychologist can put to the test in a scientific setting. An example of a hypothesis might be “The type of music playing in the background has an effect on the time it takes to complete a physical task”. The psychologist does not know if this is the case or not, but the statement is a rational prediction of what he thinks to be the case. It is also a statement of how he feels one variable is going to influence the other.
- Variables: There are usually two variables in a psychology experiment.In the example I have given one variable is the type of music the participant listens to. The second variable is the time it takes the participant to complete the task. The first is an independent variable. It is independent because the choice of music being played in the background will remain the same. The dependent variable is the one that will probably change as a result of the independent variable. In this case the dependant variable is the speed at which participants complete the task.
What are Experimental Designs?
Experimental designs are the way in which you organise your participants to test your hypothesis. You may decide to use them in one of the following three ways:
Repeated measures You have 20 participants. All of them complete the physical task whilst listening to one of the two types of music. Then all 20 complete the same task whilst listening to the other type of music. You compare the results.
Advantages: There won’t be any participant variables (see meaning below) because all participants take part in all parts of the experiment.
Disadvantages: You may get what is called an order effect. This means that people may perform the task differently the second time round simply because they have done it before and know what to expect. This may mean you have to design two different tasks, or change the order in which half of the participants do the practical task. This later strategy is called counterbalancing
Matched pairs You match the 20 participants up into pairs of similar people. One takes on an upper case letter, the other the same lower case letter i.e. Aa, Bb, Cc, Dd etc. One pair member completes the task whilst listening to one type of music, the other pair member completes the task whilst listening to the other type of music. One reason for matching people is to reduce participant variables. This occurs when the results are influenced by the skills or characteristics of the people you are using in the experiment.
Advantages: There are no order effects. You can use the same equipment all through the experiment.
Disadvantages: Matching can be time-consuming and relies on human judgement in matching people together. Participant variables may still occur.
Independent groups You split the participants into two groups. 10 participants perform the task with one type of music playing, the other 10 with the other sort of music playing. You compare the results.
Advantages: The same equipment can be used for both the trials. There won’t be any order effects.
Disadvantages: There may be some participant variables. You will usually need a high number of participants.