Cognitive and Research

Experimental Method
Key Features
Researcher manipulates the independent variable (IV) to investigate change in the dependent variable (DV)
All other variables are held constant or eliminated
Participants can be randomly allocated to conditions

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Key Terms
Variable: anything that can change/vary (eg, response times, weight, IQ scores)
Extraneous/confounding variables: any other variable that could affect the DV
Quasi-experiment: Quasi = “resembling but not really the same as” – lacks complete control (eg, natural experiment)
Independent Variable – manipulated by researcher to effect change in the DV
Dependent Variable – variable that is measured

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Evaluation of experimental method
Establishes cause & effect – only method to do this
Does not rely on naturally occurring events
Allows for study of rare events or those difficult to investigate by other means
Generates quantitative (numerical) data
Generalisability of results (but depends on sampling method used

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Laboratory experiment
Highest level of control
Can use technical or specialised equipment

Positive
Easy to replicate due to standardisation
Can infer causal relationship – due to control
Objectivity – due to levels of measurement

Negative
Artificiality – lacks ecological validity
Demand characteristics

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Field experiment
IV is manipulated by researcher – but in natural environment (eg, Piliavin’s subway study)
Used in situation when natural environment is important (eg, non-human animals)

Positive
Improved ecological validity
Reduction of demand characteristics

Negative
Difficult to establish controls – potential confounding variables
May be difficult to generalise to other situations

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Natural experiment
Quasi-experiment – lack of control
Researcher does not directly manipulate IV

Positive
Reduction of demand characteristics
Lack of direct intervention – reduces researcher bias

Negative
Loss of control – difficult to infer causality
Difficult to find suitable conditions – may be time consuming

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Aims & Hypotheses
Aim: General – tells us why the study is being conducted
Hypothesis – specific, testable statement – tells us what the study is designed to test

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Experimental hypothesis
Can be one or two tailed (also known as directional and non-directional)
One-tailed: predicts direction of results (eg, boys are faster at running than girls)
Two-tailed: only predicts a difference between the conditions (eg, there is a difference in running speed between boys & girls)

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Hypotheses contd
Predicts the effect of the IV on the DV

“Alcohol increases reaction times”
Null hypothesis: predicts no difference between conditions – therefore the IV has no effect on the DV (except due to chance)

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