12 - experimental control and internal validity

12 experimental - Threats to the Validity of Research 20:54 Good research is valid research The conclusions drawn by the researcher are legitimate

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Threats to the Validity of Research 20:54 Good research is valid research  The conclusions drawn by the researcher are legitimate  There are many threats to the validity of research, and these threats may lead  to unwarranted conclusions  There are four major types of threats to the validity of research  A threat to construct validity occurs when the measured variables used in the  research are invalid because they do not adequately assess the conceptual  variables they were designed to measure  A threat to the statistical conclusion validity of the research  Occurs when the conclusions that the researcher draws about the research  hypothesis are incorrect because either a Type 1 error or a Type 2 error has  occurred  These two threats are present even when the research is statistically valid and  the construct validity of the manipulations and measures is ensured Threats to the internal validity and to the external validity of the research  design o Internal validity: The extent to which we can trust the conclusions that have  been drawn about the causal relationship between the independent and  dependent variable o External validity: The extent to which the results of a research design can  be generalized beyond the specific settings and participants used in the  experiment to other places, people, and times
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Experimental Control 20:54 Experimental control: Occurs to the extent that the experimenter is able to  eliminate effects on the dependent variable other than the effects of the  independent variable.  The greater the experimental control is, the more confident we can be that it is  the independent variable, rather than something else, that caused changes in  the dependent variable  Extraneous Variables One cause of Type 2 errors is the presence of extraneous variables in the  research  o Extraneous variables are variables other than the independent variable  that causes change in the dependent variable  o Extraneous variables include both initial differences among the research  participants and differences in how the experimenter treats the  participants or how they react to the experimental setting  Confounding Variables Confounding variables: Variables other than the independent variable on  which the participants in one experimental condition differ systematically or on  average from those in other conditions  o Confounding variables are those that are created during the experiment  itself and that are unintentionally created by the experimental  manipulations Confounding and Internal Validity o Confounding: The other variable is mixed up with the independent 
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This note was uploaded on 11/16/2010 for the course PSYC 420 taught by Professor Staff during the Fall '08 term at Maryland.

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12 experimental - Threats to the Validity of Research 20:54 Good research is valid research The conclusions drawn by the researcher are legitimate

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