Understanding Psychology at A level and GCSE: 9: Research Design

Here is the 9th 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 – Independent Measures

When a psychologist has decided on their hypothesis and aims, they need to design an experiment to test their hypothesis.   There are three main research designs that are used in psychology experiments: –

  • Independent measures/independent groups
  • Repeated Measures
  • Matched pairs design

It is useful to know what these are. In this blog, we will look at the first research design method:

Independent Measures/Independent Groups

With independent groups, the researcher divides participants into different groups. So there may be 100 people and he/she may split them into two groups of 50 people each. So there will be different participants in both groups. This is why this method is called “independent groups”.

This method is often used when the researcher wants a control group. A control group is used to see if what is tested with the experimental group has an effect on those in that group.

For example:– We want to see whether taking a vitamin every morning for a week before an exam helps with exam performance.

So Group 1 take a vitamin tablet every morning (the experimental group).

Group 2 take a sweet every morning (the control group). They will also be told that it is a vitamin tablet. This use of a sweet instead of a real tablet is known as a placebo.

The participants in both groups think they are having the vitamin tablet.

At the end of the week, we compare the exam results of the two groups and see if there is a difference. If group 1, on average, got the best results, we might think that the vitamin tablet does have an effect on performance in the exam. Or we might find no difference on average between the two groups, or the sweet group actually does better.

There are advantages and disadvantages with this form of research method –

Advantages Disadvantages
There are no order effects – this means that the performance of participants get worse because they are tired  (fatigue effects) or that the performance of the participants gets better due to practice  (learning effects). You need twice as many participants as you do with other methods, such as repeated measures.There may be differences between the two groups, which could affect the results. For example, in the experiment above, say the 50 people in group 2 (the control group) happen to perform better in exams anyway than group 1, this could affect the result. The vitamin tablet might actually help exam performance for group 1, but these results might not show clearly if group 2 are good at exams anyway.


In the next blog, we will look at Repeated Measures designs.

Tracey Jones

Psychology Tutor

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