(2027 Exam) Variables & Control

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Variables

A key aspect of experimental research is the control and measurement of variables.

Any experiment includes two key variables:
- The independent variable — IV — is the variable that the researcher changes, i.e. manipulates. This is done by having a different value of this variable in each experimental condition.
- The dependent variable — DV — is the variable that the researcher measures.
An experiment tries to find out whether the IV has an effect on the DV.

For example, the researcher may compare the effect of using a memory technique on recall of a list of facts.
The use of the technique or not is the IV, and their recall on a test of the facts would be the DV.

To test cause and effect between the IV and DV, it is necessary to keep all other variables constant by controlling extraneous variables and minimising their effects.

Some variables can’t be entirely eliminated, such as background noise and temperature.
These are called extraneous variables.
The researcher tries to minimise the effects of extraneous variables as far as possible.
Any remaining extraneous variables are a source of random error, but do not invalidate the experiment.

Two further aspects of experimental control are counterbalancing and standardisation.

When a researcher uses a repeated measures design, participants complete two (or more) experimental conditions.
The order in which participants complete the conditions is important.
When they complete the second condition, they may do better due to practice, or worse due to boredom or fatigue.
These are called order effects, and could bias results.

Random allocation refers to the allocation of participants to conditions in an experiment (experimental condition and control condition).
This can be done by a random method such as pulling names out of a hat or tossing a coin e.g. heads – experimental, tails – control.
This is used to control for some participant variables (individual differences) in an independent measures design.

To minimise order effects, experiments use a technique called counterbalancing.
This involves allocating participants to conditions as follows:
- Half of the participants complete condition 1 first, and condition 2 second.
- The other half of the participants complete condition 2 first, and condition 1 second.
Counterbalancing does not get rid of order effects, but it stops order from becoming a confounding variable because the effect is balanced out over the two conditions.

The order of tasks or presentation of data (etc.) in an experiment or study is decided on the toss of a coin or another random method of selection to control for order effects.
- E.g. In a study (Murstein (1972)) that involves rating pictures for attractiveness, the first picture shown is likely to be given an average rating, because participants tend to rate the first picture conservatively to save more extreme ratings for subsequent pictures.

Standardisation means using a standard procedure for all participants. Things which should be standardised include:
- Giving all participants the same instructions.
- Completing briefing and debriefing in the same way and at the same time.
- Conducting the experiment in the same location and at the same time of day.
- Making sure that all materials are the same for all participants.
All aspects of standardisation are necessary to avoid extraneous or confounding variables affecting the results.

Control group is a group that does not receive the independent variable (IV).
Control group is used as a baseline for comparison with the experimental group.
Control groups help to show whether changes in the DV are caused by the IV.
- Example: Experimental group drinks caffeinated coffee; control group drinks decaf.