Understanding Psychology at A level and GCSE: 10: Repeated Measures Design

Here is the 10th in our new series of Psychology blogs – useful for anyone revising for exams or thinking about taking up Psychology as a new subject at A level or GCSE.

Research Methods – Research Design – Repeated Measures

As we mentioned in our previous blog (no.9), Repeated Measures is one of the main forms of experimental design.

Repeated measures is the term we use to describe an experiment in which all participants take part in all conditions.

For example, you want to find out whether taking vitamin tablets before an exam aids recall.

So in the first condition, you give all participants a vitamin tablet. Then you find out what percentage they got in the exam.

Then the next day, you give THE SAME participants a sweet (telling them it is a vitamin tablet) and ask them to do the exam. Then you look at what percentage they got in this exam.

Then you can compare how they did. You are using the same people, so when you compare them, you are comparing the same people, so there are no participant variables, but there can be other factors involved.

Advantages and Disadvantages of Repeated Measures Design

Advantages

• Fewer participants are needed for this type of research, but you get the same amount of data.
• You have the same people to do both conditions, so the differences should be due to individual differences affecting the results.

Disadvantages

• There is a problem of order effects. If all participants did the vitamin tablet test first, then they all did the sweet test second. It could be that when they did the second exam, they had actually got better at answering exams, so they did well in the sweet condition. So it would look as though the vitamin tablet made no difference, but in fact the results could be due to order effects.
• Let’s look at another example to demonstrate order effects.  Say you wanted to test whether eating chocolate before driving improved drivers’ speed round a track. So you asked ten people to drive round a track and you timed their results. Then you ask the SAME ten people to eat some chocolate, then drive round the track. Again you timed their results. You found that, on average, they drove ten times faster after the chocolate. So that means chocolate leads to faster driving doesn’t it? Well, not necessarily, it could be due to order effects, this was the second time they went round, so there could also be a practice effect. Really, the researcher should use counterbalancing to improve this. We will look at counterbalancing in more detail in the next blog (no.11). Counterbalancing simply means that to avoid order effects, some people would do one task first, then others would do the other task first. So some would do the driving without chocolate first, whilst others would do the driving WITH chocolate first.

In the next blog (no.11) we will look at matched pairs design in research.

Tracey Jones

Tutor