Confounding Variables

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Sometimes factors other than the IV may influence the DV in an experiment. These unwanted influences are called “confounding variables”. In laboratory experiments, researchers attempt to minimise their influence by implementing a variety of controls.

Here are some confounding variables that you need to be looking out for in experiments.

Demand Characteristics are the cues in a study (characteristics) that may lead the participant to figure out how they’re supposed to act (according to the demands of the researcher/experiment). It leads to participants behaving in a way that they think they’re supposed to, not how they would naturally. Participant expectancy effect is the name given to the change in behaviour as a result of participants behaving in a way that they think they’re expected to. In other words, demand characteristics in an experiment’s design might lead to participant expectancy effect occurring.

This is similar to the social desirability effect which is when people change their behaviour because they have a nature desire to be liked by other people. Another factor that influences people’s behaviour is when they don’t act like they normally would simply because they are being watched by someone. This was first recorded in a study on the Hawthorne Electrical Plant in the USA and has become known as the Hawthorne Effect. In the original Hawthorne Plan research they found the workers were working harder simply because they were being watched. Doesn’t this happen in the classroom? Suddenly when the teacher starts walking around the room checking work you close youtube, put away your phone, tuck away the love-letter, etc etc.

Similarly, evaluation apprehension might occur when participants are anxious about being evaluated on a particular task or skill. This might change their behaviour. Think about your oral assignments in some of your subjects, for instance. If you weren’t being graded you might be OK talking in front of your class but as soon as your teacher gets out their big red pen and beings giving you a grade on your work you’re likely to become nervous (apprehensive) and this will affect your performance. People are often nervous about being in an “experiment” because the word might conjure many scary thoughts. Imagine if you were placed in a room all by yourself and told one of two things:

a) You are just waiting here for ten minutes and the interviewer will be here shortly

or, you were told:

b) The experiment has begun. Please wait here for ten minutes.

Which would make you more nervous? Would you behave equally in both?

One reason people might change their behaviour when being studied is because humans tend to have a natural desire to be liked. People want to be liked and so they may alter their behavior so they are not viewed negatively or foolishly. This is called the social desirability effect. For example, in an interview about stereotypes, participants may not be honest about stereotypes the have through fear of being viewed as racist.

In repeated measures experiments one must be careful of order effects. Sometimes the order in which a participant does a task may alter the results. For instance, they may get better with practice and this could disrupt the results, or they remember something from the first condition that may alter their results. This is similar to maturation, where participants get better on the second or third trial simply because they have practiced the skill. Maybe contamination could occur which is when outside information affects the results of the experiment.

Counterbalancing is one way of controlling for order effects. Counterbalancing is when repeated measures is used but half the group do Condition A then Condition B and the other half do it in the opposite order. Using an independent samples design also controls for order effects.

Participant variability is the extent to which participants are different and is another potential factor that could influence an experiment’s results. For instance, in a study on the effects of a new training technique on fitness levels the existing fitness of the participants might be quite varied. This can easily be controlled for though either using random allocation or a matched pairs design.


What confounding variables can you find in this experiment?


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