21 - Lecture- Tuesday 5-19-09 Problems with Participants...

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Lecture- Tuesday 5-19-09 Problems with Participants Reactivity Effects o P’s reaxtion to being studied rather than to treatments, influences DV Hawthorne effect- when participants are being watched, so people do whatever it is more Placebo effect- false treatment makes people think it’s happening Demand characteristics- reactivem thgink they know what you want them to say … are always possible threats if only one group, or if have unequal groups How to control reactivity? o random assignment to proper groups/ condutions (ie conduct a true experiment o R X O (group 1) R O1 X O2 (group 1) o R X O (group 2) R O1 O2 (group 2) o Treat groups equally-- control groups get equal time, attention, etc o Participants should be “blind” to condution --effects related to pre-testing: -testing/sensitization effect-- now they’re thinking about it -Maturation-- even without doing anything, there is natural fluxuation from time 1 to time 2 -mortality (attrition)-- people who don’t come back --How to control these problems? -again, random assignment to proper conditions (eg pre/post control group design- has equal groups, all with pretests, etc.) Problems with Procedure:
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o Selection bias- different group dynamics…
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21 - Lecture- Tuesday 5-19-09 Problems with Participants...

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