The research design refers to the overall strategy that a researcher chooses to investigate the research problem and test their hypothesis. The research design a psychologist chooses may have an effect on the validity of the study.  The two most commonly used designs that we see in IB Psychology are the repeated measures and independent samples design.  However, it is important for you to know that other research designs exist since you will find an example of other ways of doing research throughout the course.

Repeated measures design

In a repeated measures design, you have one sample of participants that receives each condition of an experiment.  If we were testing the effect of music on learning, the same participants would memorize a list of words with music - and then again without music.

It is not always that there are two or more conditions that are tested distinctively.  Sometimes researchers test the conditions concurrently - that is, at the same time.  For example, a psychologist may give a list of words to a group of participants to memorize.  Some of the words are about childhood and the other words are about adulthood. The psychologist wants to see if one type of word is recalled at a higher frequency than another.

The strength of this design is that an individual is only compared to him or herself.  In other words, participant variables are controlled. In the example of having to memorize a list of words while listening to music, an individual's level of English will not make a difference because she is only being compared to herself, not to someone who speaks English more fluently. Another advantage of this design is that fewer participants are needed.

There are also limitations to this design. When participants are asked to take part in more than one condition, they may demonstrate what is called order effects.  For example, boredom, fatigue, or practice effect.  Practice effect is when they get better at something just because they keep doing it.  If they are given a memory test four or five times, they may just get better because they are developing strategies through practice.

Researchers can control for order effects by counter-balancing. This means that one group of participants will start with condition A and then takes part in condition B. The second group of participants starts with condition B and then takes part in condition A.  This makes sure that it is not the order of the conditions that affects the results of the study.

Another limitation is that participants may demonstrate demand characteristics -  that is, participants form an interpretation of the experiment's purpose and subconsciously change their behaviour to fit that interpretation.  They may try to do what they think that the researcher wants them to do - a demand characteristic called the expectancy effect.  Or they may try to disprove the hypothesis with a demand characteristic called the screw you effect.

In repeated measures designs it is often not possible to use the same materials for both conditions. For example, you cannot use the same list of words to memorize under two conditions.  By using two different lists of words, you now have introduced a confounding variable - for example, the difficulty level of the words may be different or some of the words may be more familiar to an individual in one condition than the other. Confounding variables - also called extraneous or third variables - lower the internal validity of an experiment, making it less clear whether it was actually the independent variable that influenced the dependent variable.

Independent samples design

In an independent samples design, members of the sample are randomly allocated to one condition of the experiment. If we were testing the effect of music on learning, the participants could be randomly assigned to the classical music, rock music, pop music, or no music condition.

The strength of this design is that order effects are controlled for since each participant only experiences one condition. In addition, demand characteristics are less likely as the participants will most likely not guess the hypothesis.  Finally, the same materials can be used for all conditions - for example, the same list of words could be used for each of the groups as they listen to different types of music.  Therefore, we could draw a conclusion about the type of music used since all participants were given the same list of words.

As with any design, there are limitations. Unlike the repeated measures design, participant variability may influence the results of the study. - for example,  one group may have more non-native English speakers or better memorizers. Another difficulty of using an independent samples design is that more participants are required.

Matched pairs design

A matched pairs design is an independent samples design in which participants are not randomly allocated to conditions. Instead, they are usually pre-tested with regard to the variable. So, a memory test may be given and then the weakest memorizers are randomly allocated to one of the conditions, then the middle performing memorizers are allocated, and then the top-performing memorizers.  In this way, the researchers guarantee that each condition has the full range of ability.  Random allocation may end up with all of the poor memorizers in a single group. In this way, we lessen the chance that participant variability will affect the results.  It could also be that they are "matched" based on a trait - for example, years speaking English, whether they do regular exercise or if they are a smoker.

Checking for understanding

Qualitative research methods