Research methods and statistics
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Internal validity is concerned about the
causal-effect relationship in a study
◦ Can observed changes be attributed to your
programme/intervention or are the results
influenced by alternative causes?
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Three types of threat:
◦ Single groups
◦ Multiple groups
◦ Social interactions
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History – some historical event that occurred
Maturation – events over time that aid learning
Testing – pre-testing primes the participants
for what is to come (practice effect)
Instrumentation – is there any difference in the
pre-test/post-test instrument. What
information do we have on reliability, or has
the instrument been modified
Mortality – have any participants dropped out
Regression- pre-test scores are always likely to
improve on a post-test
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Have a control group that does not have the
programme/intervention
◦ Placebo effect in medical trials
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Selection bias – the degree to which the
groups are comparable before the study
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Selection
Selection
Selection
Selection
Selection
Selection
history threat
testing threat
maturation threat
instrumentation threat
mortality threat
regression threat
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Conduct a randomised or true experiment
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Diffusion of treatment – participants share
their experiences with other participants
Compensatory rivalry – groups try and
compete with one another
Resentful demoralisation - the comparison
group under achieves due to jealousy with
the other group
Compensatory equalization of treatment the researcher tries to make one or both
groups feel special
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External validity is concerned with
generalisation
◦ Can you generalise your results to a wider
population
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Sample modelling – you first identify the
population you want to generalise to and
then draw a sample from that population
Proximal similarity (Gradient of similarity) –
identify populations that are more or less
similar to the original study
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Unusual people
Unusual places
Unusual times
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Use a random sample
Keep drop out rates low
Replicate the study with different people at
different times in different places
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Electronic resources are available from
◦ http://www.socialresearchmethods.net/kb/contents.php