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chapter 6 validity .pdf

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Psychology 2800E
Doug Hazlewood

Chapter 6- McBurney Validity- an indication of accuracy in terms of the extent to which a research conclusion corresponds with reality. Four types of validity- internal, construct, external and statistical conclusion - Internal validity is the most fundamental type because it concerns the logic of the relationship between the independent and dependent variables. In an experiment with high internal validity, it really was the independent variable that caused the dependent variable. Internal validity- extent to which a study provides evidence of a cause and effect relationship between the independent and dependent variables • confounding- error that occurs when the effects of two variables in an experiment cannot be separated, resulting in a confused interpretation of the results (i.e. testing one group Mon. morn, another Wed. night) • the problem of confiding is particularly acute in research in which the experimenter cannot control the independent variable- when participants are selected according to the presence or absence go a condition and not selected simply to have a condition assigned to them. Such variables are called subject variables (i.e., gender) Subject variables- a difference between subjects that cannot be controlled but only selected Construct Validity- extent to which the results support the theory behind the research • for example, does an IQ test really measure intelligence or does it measure economic status? - to improve construct validity you might use a manipulation check; an aspect of an experiment designed to make certain that variables have changed in a way that was intended. - a good manipulation check is the Beck Anxiety Inventory - main purpose of construct validity is to rule out other possible theoretical explanations of the results (i.e. in rat experiment where rat gains weight after damaging their hypothalamus- originally thought that this increased a rats hunger, when there were in fact many other feasible possibilities i.e. this decreased the rats satiety, or changed the rats metabolism) External validity- how well the findings of an experiment generalize to other situations or populations - note 1949 experiment where people took longer to say taboo words flashed on a screen; could not be generalized to todays world as many words that were taboo then are not taboo now (lacked external validity) Ecological validity- extent to which an experimental situation mimics a real-world situation - a way to increase validity in the word study would be to have participants experience all words, including taboo ones, in a way that words might be normally encountered, such as in a reading a story aloud Statistical Conclusion Validity- extent to which data are shown to be the result of cause-effect relationships rather than accident - here the question is, did the independent variable truly cause a change in the dependent variables or was the result accidental, and thus caused by pure chance? - to establish statistical conclusion validity, appropriate sampling and measurement techniques must be used, and inferential statistics must be used properly, in keeping with their underlying assumptions. - must also test enough people so study has adequate power Power- the probability of rejecting the null hypothesis when it is, in fact, false - if an experiment suffers from lack of power, the experiment may appear to show that the null hypothesis is supported, when in reality, it should be rejected Effect size- strength of the relationship between the independent and dependent variables - the magnitude of the cause and effect relationship goes beyond simply saying that the relationship is significant and can help to establish whether a significant result is of practical importance Threats to Validity Threats to Internal Validity • Ambiguous temporal precedence- although two variables are related, it is not clear which one is the cause and which one is the effect (i.e. poverty level and performance in school) • Events outside the lab (History)- events that occur outside of the experiment that could influence the results of the experiment (if you studied the effects of success and failure on feelings of depression and all of the participants experienced the failure condition on Monday and the success condition on Wednesday, you can imagine that the results would be difficult to inte
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