Manipulation and Control of Variables (AQA A Level Psychology)
Revision Note
Written by: Claire Neeson
Reviewed by: Lucy Vinson
Independent & dependent variables
In an experiment, a variable is any factor that could change or be changed
There are different types of variables within an experiment
The independent variable: the only variable that should be changed or manipulated throughout an experiment
The dependent variable: the variable that is measured to determine the outcome of an experiment (the results)
Independent variables
The IV is required to observe the effect it has on the dependent variable (DV), which is the variable being measured
Examples of independent variables:
Whether participants learn a list of 20 words in silence or learn the words in the presence of loud rock music
The IV = silence or loud rock music
Whether participants complete a jigsaw puzzle after 30 minutes of exercise or complete the puzzle after no exercise
The IV = 30 minutes of exercise or no exercise
Whether participants have been exposed to an aggressive model or have not been exposed to an aggressive model
The IV = aggressive model or no aggressive model
A laboratory experiment must use an IV that has been implemented by the researcher e.g. loud music or silence
The IV cannot be naturally occurring e.g. gender, age, ethnicity
Any experiment which uses a naturally occurring IV is known as quasi/natural experiments
Dependent variables
The dependent variable is the factor which is measured in the study to assess the effect of the IV
Examples of dependent variables:
The number of items recalled from a list of 20
The time taken in seconds to complete a jigsaw puzzle
The number of imitative acts of aggression performed in a 20-minute observation schedule
The DV depends on how the IV has been set up
If the IV is memorising items with loud music or in silence then it makes sense that the DV is ‘the number of….’ or ‘the time taken to…’
Thus the DV must be measured using quantitative data
It is impossible to have a qualitative DV:
The measure will always take some form of numerical data, which can then be displayed in a graph and analysed statistically
Qualitative research collects data in the form of words
Operationalising variables
Operationalising variables refers to how both the IV and the DV are put to work/implemented by the researcher (see also revision notes on hypotheses)
Operationalising variables involves specifics on how each variable is to be manipulated (IV) and measured (DV)
Operationalising the IV
To operationalise the IV the researcher needs to set up and define each condition so that it is clear that a difference between the conditions is being investigated
E.g. participants in condition 1 drink 200ml of a caffeinated drink prior to a memory test; participants in condition 2 drink 200ml of water before a memory test
The IV is broken down into two separate conditions, (200ml of caffeine or 200ml of water), each of which is clear from the wording provided
Operationalising the DV
To operationalise the DV the researcher needs to design a procedure which enables relevant and appropriate data to be recorded/collected per participant with no ambiguity involved
E.g. the number of correctly recalled items from a list of 15 words
The DV provides the number of total possible correct answers (15) and identifies how participant performance is to be measured (number of correctly recalled items) with no ambiguity involved
Extraneous variables
Extraneous variables are any factors that intrude upon and adversely affect the DV (not the IV, which the researcher has specifically implemented) e.g.
time of day
some participants may be 'morning people' which means that they are likely to be more alert first thing compared to others
temperature
if the experimental space is too warm/cold it may affect participant performance on the task
mood
one participant may have just had a row with their partner or won some money or feel a bit ‘off’ that day: any of these events mean that their mood is likely to affect their performance on the task
Extraneous variables are usually controlled so they have the same effect across all conditions, which should stop them from affecting the DV, e.g.
time of day
run the experiment at midday which should hopefully be a neutral time for everyone
temperature
ensure the experimental space has an ambient temperature
mood
treat participants in a pleasant but neutral way
It would be impossible to control every potential extraneous variable during the experimental phase but it is the researcher's responsibility to do all that they can to ensure that their research is objective and unbiased
If extraneous variables are not controlled then they can become confounding variables
Confounding variables
Confounding variables can affect the DV and negatively impact the research findings
Extraneous variables which - if not controlled - can become confounding variables as follows
time of day
the researcher runs each trial/condition of the study at 8 am which means that many of the participants are not able to concentrate fully as they feel sleepy
temperature
the experimental space is too cold as the researcher has not prepared an ambient temperature which means that participants are more focused on keeping warm than on completing the task properly
mood
the researcher is overly friendly with the participants, making jokes and laughing a lot, which affects the participants' mood (some of them feel good as a result; some of them feel annoyed as a result)
The interference of confounding variables may not be apparent until after the research process has been completed
If this is the case then the researcher should acknowledge the possibility of confounding variables in the discussion section of the psychological report
Examiner Tips and Tricks
It is very important to ensure that you don't confuse the independent variable with the dependent variable (it is amazing how many students do this every year!) Just keep telling yourself that the DV depends on how the IV has been implemented.
You may also be asked in an exam how a researcher could control potential extraneous variables. If you are asked this question, remember to actually answer it (sounds obvious, but...)! If you simply identify potential extraneous variables without actually explaining how they could be controlled then you would not receive full marks (in fact you may not be awarded any marks if the question only asks you about the control of variables).
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