Chapter 8 - Skeleton - Psy250 Scientific Inquiry Chapter 8...

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Experimental Design Psy250: Scientific Inquiry Chapter 8
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Notes About Attendance Assignment From Last Class Probability sampling: simple random sampling: get list of all UB students then randomly select students from the list ( random # generator, computer program, draw names out of hat). Randomly selected students are surveyed. Stratified random sampling, would still need a list of all UB students. This time are divided into subgroups ( strata) . Might subgroup based on major, year in school, place of residence,etc. subgroups should be meaningful to your question of interest. Cluster sampling: would not require having a list of all UB students. Could instead get a list of classes. Non probability sampling: just sample whoever. Purposive: maybe decide some reason on sampling ( age) Quota,. . UB student body 2/3undergrad and 1/3 grad. Using quota sampling could make sure our sampling is roughly 2/3undergrad anmd 1/3grad.
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Recall… In experimental method all extraneous variables are controlled In experimental method there should be no differences between groups (or conditions) other than the experimental manipulation Experimental methods allow relatively unambiguous interpretation of results
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Recall… In experimental methods researcher manipulates independent variable to create groups that differ on levels of variable Compare groups in terms of scores on dependent variable Other variables kept constant through experimental control or randomization If scores on dependent variable differ across condition, can say independent variable caused these differences
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Confounding and Internal Validity Confounding variable: variable that varies along with independent variable. -Effects of independent variable and confounding variable are intertwined-> can not determine which is responsible for observed effects .
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Confounding Variable Example A reseracher wants to show that students who try to learn large amount of material all at once don’t do as well as those who spread their learning over several sessions. Three groups of students are selected and each group is given the same chapter in a general
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Confounding and Internal Validity A good experimental design involves eliminating possible confounds - do not want to have any potential alternative explanations! Internal Validity:
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This note was uploaded on 03/10/2011 for the course PSY 250 taught by Professor Briannalharris during the Summer '10 term at State University of New York.

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Chapter 8 - Skeleton - Psy250 Scientific Inquiry Chapter 8...

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