Controlling of variables

Psychology AS · Research methodology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

A researcher wants to be sure that the independent variable, and nothing else, caused the change in the dependent variable. To do this, other variables that could affect the DV are kept the same for every participant. These are called controls.

An uncontrolled variable is one that is not kept the same and may affect the DV, so the results are less valid. Participant variables are differences between people, such as age, intelligence or mood. Situational variables are differences in the setting, such as noise, temperature or time of day.

Standardisation means every participant has the same procedure, instructions, materials and timing. This makes the study fair and easy to repeat.

Rules to remember

Control: keeping a variable the same in all conditions so it cannot affect the DV.
Uncontrolled variable: a variable other than the IV that may affect the DV.
Participant variables: differences between individuals, e.g. age, ability, motivation.
Situational variables: differences in the environment, e.g. noise, lighting, time of day.
Standardisation: the same procedure and instructions for every participant.
Random allocation to conditions reduces the effect of participant variables in independent measures.
Repeated measures removes participant variables between conditions; counterbalancing deals with order effects.

Common mistake

Students label a difference in the room or the time of testing as a participant variable. If it is about the setting it is situational; if it is about the people it is a participant variable.

Worked example

In a test of whether chewing gum improves concentration, the gum group is tested at 9 am and the no-gum group at 4 pm. What is the problem and how can it be fixed?

The IV is gum or no gum, but the time of day also differs between the groups.
Time of day is part of the setting, so it is an uncontrolled situational variable.
Tiredness at 4 pm could lower concentration, so the effect of gum cannot be separated from it.
Control it by testing both groups at the same time of day.

Answer: Time of day is an uncontrolled situational variable; test both groups at the same time.

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