Experiments Notes - AS OCR Psychology Unit 1

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Psychology Notes Experiments
Types of Variables
Independent Variable ­ The variable that is manipulated by the investigator
Dependent Variable ­ The variable that is measured
Control Variables ­ Variables that are controlled during the investigation
Extraneous Variables ­ Variables that have the potential to confound the study if they are
not controlled for ­ Any other variable other that the IV that may affect the DV
· Participant variable (Individual differences) ­ May be countered by using an
repeated measures design or a matched pairs design
· Situational Variables (Features of the situation which may affect the
participant's behaviour) ­ May be countered by using an independent measures
· Order Effects (A type of situational variable where the participants may
become bored or fatigued after completing the same task more than once) ­
May be countered by using an independent measures design or counterbalancing
(when each condition is tested first or second in equal amounts)
· Investigator Bias (When the investigator's expectations affect the behaviour
of the participant) ­ E.g. if the investigator encourages certain behaviours ­ May be
countered by standardized instructions (all participants have the same
instructions) or single blind (participants are not told the true aims and cannot look
for clues)
Operationalizing variables = To specify a set of operations or behaviours that can be measured or
manipulated and to be explicit about each variable so that the experiment may be replicated.
Onetailed Hypothesis ­ A hypothesis that states the expected direction
Twotailed Hypothesis ­ A hypothesis that does not state the expected direction
Null Hypothesis ­ A hypothesis states that there is no difference/relationship
Experimental Designs
Independent Measures Design ­ When each participant takes part in all conditions
No order effects
Prevents situational variables e.g. time of day confounding a study
Reduces the likelihood of participants responding to demand characteristics
May be affected by individual differences

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Repeated Measures Design ­ When each participant is tested in only one of the
No individual differences
Fewer participants needed
More likely for the IV to be discovered (more likely to respond to demand
Participants may experience boredom/fatigue (order effects)
Matched Pairs Design ­ Where the participants are matched on key personal variables
e.g. age, gender, ethnicity etc.…read more

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Having multiple observers DOES NOT automatically increase interrate reliability ­ they must be
trained to observe the same things in the same way
Validity in Experiments
Control ­ Failing to control extraneous variables may mean that it is not the IV affecting the DV
and the experiment is not valid
Ecological Validity ­ The extent to which findings of a study can be generalized to everyday
· Higher ecological validity = more generalizable
· Lower ecological validity = less generalizable
Experiments can be…read more


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