Extraneous variables can be caused by the environmental conditions (e.g light, noise, heat etc) , the characteristics of the participant (emotional state, sex,age etc) or the characteristics of the task (the instructions, the way the stimulus materials are presented etc).
All of the above conditions are fine as long as they are either held constant or randomised across the conditions of the research
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Confounding Variables
This is a variable which has an unintentional effect on the dependent variable
When carrying out experiments we attempt to control extraneous variables, however there is always a possibility that one of these variables is not controlled and if this affects the dependent variable in a systematic way or it only affects one aspect of the experiment, we call this a confounding variable.
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Order Effect
This is when the order in which the different tasks of the research are carried out interfere with the performance of the participant.
It could be that the participant will do better on the second task due to practice or will not do as well due to fatigue, causing the results to be ineffective as it will not be clear as to what is affecting the outcomes of the research.
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Experimenter Effect
Experimenter effect is when the researcher has a direct impact on the results of the sudy.
They may guide the participant to perform in a way that supports the aim of the research so encourage them to do better in one task but not the other (intentional or unintentional).
The personality or gender of the researcher may also affect the outcomes of the research as they may be perceived to be more or less friendly by the participant which could then affect the participant's performance.
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Participant Variables
Participant variables are aspects of the participants' characteristics or experiences that could affect the outcomes of the research.
This may be something specific such as eye sight that could affect how they perform on a reading task or age as they may have different past experiences again, affecting task completion.
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Situational Variables
Situational variables are aspects of the research situation that could affect the outcomes.
This could range from the weather which could affect concentration levels to the colour of the chairs the participant is sitting in as they may make the participant uncomfortable
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Counterbalancing
One way of controlling 'order effect' in a repeated measures design is by counterbalancing the order of tasks which participants are asked to complete.
This means that one half of participants would complete the task in condition 1 before completing the task in condition 2 and the other half of pps would complete the tasks in reverse order.
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