Lesson 8: Control of Extraneous Variables

Question 1

Why must extraneous variables be controlled?

Answer 1

To ensure a study has validity, extraneous variables must be controlled to prevent them from becoming confounding variables.

Question 2

Participant variables

Answer 2

Characteristics of the participants which may affect the dependent variable (e.g. intelligence, age, gender, personality etc). Choosing an appropriate experimental design can help to try and overcome these types of extraneous variables.

Question 3

Matched pairs and repeated measures

Answer 3

Can help to avoid participant variables. However, repeated measures can lead to order effects, so counterbalancing should be used to avoid this.

Question 4

Random allocation

Answer 4

Random allocation of participants to conditions (e.g. drawing names out of a hat) when using independent groups should also ensure that groups are not biased. However, random allocation is not possible for a quasi experiment.

The process of random allocation involves all the participant being identified either by name or number. The names are put in a container or into a computer. Assign alternates numbers drawn to condition 1 and then condition 2 and so on until there are the required number in each condition. Alternatively, set the parameters on the computer from two groups to be randomly generated.

Question 5

Environmental variables

Answer 5

Factors in the environment where the experiment is conducted that could affect the DV (e.g. temperature, time of day, lighting, noise).

The solution to this is standardisation- making sure that all the conditions, materials, and instructions are the same for all participants.

Question 6

Investigator effects

Answer 6

When the person collecting the data has knowledge of what the research aim is and that knowledge affects the data obtained. Observer bias is a type of investigator effect.

Investigator techniques can be overcome by the double blind technique- when neither the participants nor the investigator know the hypothesis of the study or what condition the participant is in.

Investigators may influence the results of their research. Certain physical characteristics of the investigator, such as age, gender and ethnicity can influence the behaviour of participants. Standardised scripts should be written to ensure that the investigator acts in a similar way with all participants. The investigator should be trained to greet all pps in the same way and ask them questions in a neutral tone. For some studies it may be necessary for the pps and researcher to be of the same gender.

Question 7

Demand characteristics

Answer 7

• Common extraneous variable
• There are features of a study which enable the participant to guess the study’s purpose and what is expected of them
• Can lead to pps trying to please the researcher by giving the ‘right’ results, trying to annoy the researcher by giving the wrong results, acting unnaturally out of nervousness, or acting unnaturally out of social desirability bias.
• Observer and interviewer effects are demand characteristics
• Can be overcome by the single blind technique- when pps do not know the hypothesis or what condition they are in