PSY 313 Week 9 Notes
PSY 313 Week 9 Notes PSY 313
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This 4 page Class Notes was uploaded by Bria Harris on Wednesday October 28, 2015. The Class Notes belongs to PSY 313 at Syracuse University taught by Amy Criss in Summer 2015. Since its upload, it has received 36 views. For similar materials see Intro. to Research Methodology in Psychlogy at Syracuse University.
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Date Created: 10/28/15
PSY 313 Week 9 Lecture Notes October 26th and 28th Pepsi Challenge refer back to last lecture notes Pepsi wins BUT label was confounded IV Beverage DV Preference ratings Extraneous Variable EV gender height hair color Confound label Does Darkness Affect Memory Performance Undergraduates given a memory test at 2 PM light amp 2 AM dark amp performance was worse at 2 AM Therefore darkness impairs memory Is this a valid interpretation Any confounds that prevent this interpretation 0 IV Time 0 DVMemoryPerformance 0 Everyone in the 2 AM condition is sleepier than everyone at the 2 PM condition systematically related Depression Treatment Depressed patients given medication for depression beginning in February In June level of depression measured again amp it s lower than the levels in February Therefore medication alleviated depression People are generally happier in June than they are in February more sunshine 0 IV Medication 0 DV Depression More Examples Hypothesis light causes rat to become agitated Example 1 Don t know if this light is agitating or sound is calming Example Sometimes when the light is on the sound is off no relationship no systematic relationship Common Threats to Internal Validity Confounds History Uncontrolled events that happen mid experiment eg construction with Dr Criss experiment Maturation Participant changes over time Instrumentation Change in the ability to use information or in the measurement device itself SelectionAssignment Selfselection or improper assignment to condition Testing effects Change in performance due to practice or fatigue with the material Introduction to Experimental Methods Recall that Causation Requires Correlation DirectionalityTemporal Precedence Cause must come before the effect Experiment can enforce precedence by manipulating a variable Eliminate other explanations Through experimental control If successful then strong internal validity Elements of Experimental Design Manipulation Change variable to create multiple treatment conditions IV Measurement A variable is measured for each condition DV Comparison Score in one treatment is compared to scores in another treatment 0 Consistent difference evidence for causation Control All other variables controlled 0 Eliminated confounds What is Experimental Control A set of tools to allow an experimenter to eliminate confounds amp to ensure that the IV is causing changes in the DV not something else Tools for eliminating systematic variation 1 Holding constant 2 Matching 3 Random Assignment Control groups Review IV DV Extraneous Variable EV variable not controlled or manipulated adds random noise Confound systematically varies with the IV amp can explain the results Controlled Variable held constant equal the same across levels of the IV because it is a suspected confound Example Does larger shoe size cause an improvement in reading ability 0 IV Shoe size 0 DV reading ability 0 Levels Size 4 vs Size 6 o Confound Age Holding Constant Hold the value of a potential confound constant across all levels of the IV All items have the same value or a restricted range Shoe size reading ability age everyone is 8 years old Matching If you have identified a possible confound Match participants or stimulus material on that confounding variable across the levels of the IV For every level of the IV there exists one item person with the same value of the potential confound Shoe size reading ability Size 4 5 of each 5yearold 55 Year old 6 year old 65 year old etc Size 6 Same as above Different levels of IV Random Assignment Sampling How we select people from the population Assignment How we place that sample into the conditions of the experiment levels of the IV randomly assign people to particular conditions For each participant from the sample randomly assign them to condition ip coin random number generator Any difference between individuals should bequot equally spread across conditions by chance Shoe size reading ability not possible because confound exists in the person can t change age Random Assignment Random Assignment Any difference between individuals should bequot equally spread across conditions by chance Matching A tightly controlled way to cancel out differences in a potential confounding variables Often times we use both Match one or 2 highly important variables Randomly assign the rest Control Groups Eg Taking dance lessons DV Measure waltzing ability If we see high scores on the DV can we say that lessons improved performance If so by how much