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Experimental Methods

Laboratory experiment
Used to test a difference/causal relationship, NEVER a relationship!

Identifying a Laboratory Experiment:
Controlled conditions to reduce extraneous variables
IV and DV are manipulated
Measures taken carefully

+ Replicable
+ High control over variables = high internal validity

- Artificial environment = lacks internal…

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Identifying a natural Experiment:
Naturally occurring independent variable
i.e. research if seaside's are more fun than theme parks. The seaside is the naturally occurring
IV because the experimenter did not make them and they occur naturally.

+ real world environment = high ecological validity
+ No demand characteristics


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Make sure any hypothesis is fully operationalised

NEVER begin a hypothesis with `I predict/believe/think'!

Directional hypothesis: use only when there is previous research to justify it. Begin it `[insert]

Non-directional hypothesis: always use. Begin it `there will be a difference/relationship...'

Null hypothesis are only used in research reports. If…

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+ No effect by individual differences ­ each person takes part in each condition
+ Inexpensive (don't need as much participants)

- Order effects:
- Practice effects: if the conditions are similar, then doing one condition will improve their
performance in the other condition
- Boredom effects: if…

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Identifying a correlational analysis:
No IV or DV, just covariables

Correlation coefficient
-1 = strong negative correlation
0 = no relationship
+1 = strong positive correlation

+ a relationship between two variables can be confirmed. This could lead to further, more substantial

- no cause and effect…

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+ Social desirability
+ Biased sample ­ people of a helpful nature may only be interested in answering the questions
+ Can be biased by leading questions

+ more insightful data compared to questionnaires
+ Simple and fast, can be conducted by anyone

+ Social desirability…

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This technique involves observing subjects in their natural environment. A controlled observation or
experiment is not used because it is important to have ecological validity.

Behaviour Category
Choose the behaviours/variables you need to look for
and operationalise them so to have inter-rater reliability.
These behaviours will appear on a behaviour…

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Questionnaires ­ Do participants understand the questions? Are the questions flawed?

Control of extraneous variables

Extraneous variables are variables you try to control for before/while the study is taking place

Confounding variables are variables that have affected the experiment after it has taken place

Controlling for EV:
- Random sampling/assignment…

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i.e. all participants receive the same biology text book
- Control group
- Replication

Reliability: Consistency over time or between different tools or measures

Inter-rater reliability (observer reliability): the degree of agreement between different observers.

Using correlations to assess inter-rater reliability
Comparing the observations of the observers is best…

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between two observations of the same event then you can confidently say that you have good
observer reliability.

Improving inter-rater reliability
- Operationalising
- Training: good observation skills to easily identify the appropriate behaviours
- Same view of behaviours: i.e. view same video or angles

Test reliability: the extent to…





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