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Research Methods - External Validity.docx

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University of Guelph
PSYC 2360
Naseem Al- Aidroos

Research Methods - External Validity Validity Threats  Construct validity - measuring thing you think you are measuring  Statistical conclusion validity - whether or not you are rejecting null hypothesis and how often you are incorrect in doing so  Internal validity - to what extent you can conclude independent variable is causing dependent variable  External validity - extent to which results can be generalized beyond the specific way of the original experiment When can we generalize to other people?  True generalization is not possible because it is impossible to draw a truly representative sample of all human beings o Frequently assume that unless there is a reason to believe otherwise, relationships between conceptual variables found in one group tends to also appear in other groups too o Burden of proof rests on those who claim that a result will not generalize to demonstrate that this is indeed the case  Tough question o Theoretical question  Phenomenon (but be careful here)  Can reason about it, things that tend to have better external validity… o Large sample sizes that characterize the population at large o Evolutionary psychology - we have faster perception of colour red  Things that vary between cultures are hard to generalize and say it has high external validity  Characteristics of population under study  What is different about this population compared to other populations  Problem with using college students - might be cognitively different, have a higher need for approval o Empirical question  Go and find out - much easier to do  To make strong claim that you expect to find something in one population and not in another you are going to have to go out and do it  Have to make sure it is worth it, does it matter to you? When can we generalize to other settings?  Extent to which research will generalize beyond specific settings and techniques used in original study o Uniqueness of one experiment makes it possible that findings are limited in some way to the specific settings, experimenters, manipulations or measured variables used in the research  Tough question o Repetition with variation in study  Does it generalize across psychological conditions o Focus on ecological validity (make sure that various settings you have tend to occur in everyday social / psychological world) o Field experiments - experimental designs conducted in natural settings  Possibility of more ecological and consequently, more external validity  Influence of extraneous variables can noise the data  Greater potential for random error and systematic error that would not happen in a lab  Practicality?  Sometimes hard for research to go into the field and think of strong manipulation that you can actually get away with  Cannot always get permission to conduct them and even if access is gained it may not be feasible to use random assignment  Natural?  How can you do something that will still appear natural after the experimental manipulation? Importance of Replication  Necessary in order to conclude external validity  Ways you can replicate: o Exact replication - do the same experiment twice  Does it happen?  Not good enough to get something once - often used to see if same effect can be found in another lab with another researcher  Technically no such thing because would at least be using different participants o Conceptual replication  Different operationalizations lead to the same result?  Exact replication with creativity built in  If same relationship can be demonstrated with different manipulations or different dependent measures the confidence that the observed relationship is not specific to the original measures is increased  If same findings not found, might give us information about when effect occurs  Sometimes d
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