chapter 6 class version b
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TRANSCRIPT
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Chapter 6: Research Validity
Continued10/2/2012
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Road Map
• Turn in Reflection Assignment #1• Announcement about lab• Quick Review• Finish Chapter 6
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About Lab
• Go to class• Turn in assignments• Starting group project this week—you can’t
contribute fully if you aren’t there!• Remember: can be dropped after 4 absences• If you fail lab, you fail the course• Pay close attention to detail
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Quick Review
• Statistical Conclusion validity• Construct Validity– Threats: participant reactivity
experimenter effects (will discuss next)
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Construct Validity
Criterion-Related Validity
Predictive Concurrent
DiscriminantConvergent
Content-Related Internal Structure
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Threats to Construct Validity
• Factors that impact how well our operationalizations actually represent constructs
• Pg 171, Table 6.2 – long list of threats
• We will focus on two major ones:– Participant reactivity to the experimental situation– Experimenter effects
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Participant Reactivity to the Experimental Situation
• Participants’ motives and perceptions
• Demand characteristics
• Positive self-presentation
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Instruction set #1
We want to see how well you are able to learn the following sets of letters. Letters will appear in groups of 3 to 7, and each letter will appear on the screen for 1 second. Following the presentation of the letters, …
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Instruction Set #2
In the following task, you will be presented with groups of letters ranging from 3 to 7 letters. Each letter will appear on the screen for one second. Your task is to…
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Experimenter effects
• Researcher actions and characteristics that influence the responses made by the research participant
• Expectancies– Clever Hans
• Attributes– Biosocial– Psychosocial– Situational factors
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Clever Hans
I Math
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Internal Validity
• The extent to which we can accurately infer that the independent and dependent variables are causally related
Observed Effect (DV)
Independent Variable
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Causally Related
Independent Variable
Observed Effect (DV)
Cause must precede effect
Cause and effect are related (covary)
No other explanation is plausibleNo other explanation is plausible
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Special Considerations
• Extraneous variables
• Confounding extraneous variables
• Control
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Threats to Internal Validity• History • Maturation • Instrumentation • Testing • Regression Artifact • Attrition • Selection • Additive and Interactive Effects
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History
• Any event occurring after the study begins that could produce the observed outcome
• Differential history: only one group experiences history event
• Note what history is NOT
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Maturation
• Changes in biological and psychological conditions that occur with the passage of time – Factors within the individual
• Example: Head Start program and achievement over a school year
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Instrumentation
• Changes in the assessment/measurement of the dependent variable
• Example: multiple observers and interviewers
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Testing
• Changes in a person’s score on the second administration of a test are a result of previously having taken the test
• Example: pre-test and post-test on memory task
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Regression Artifact
• a.k.a. regression toward the mean
• The tendency for extreme scores to become less extreme on a second assessment
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Attrition
• Participant drop-out– Don’t show up for appointment– Decide to discontinue study
• Differential attrition is especially problematic
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Selection
• The choice of participants for the various treatment groups based on different criteria – NOT random assignment
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Additive & Interactive Effects
• The combined effect of several threats to internal validity
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External Validity
• The extent to which the results of the experiment can be generalized across variations in:– people– Settings– Treatments– Outcomes– Time
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What Limits External Validity?
• Lack of random selection/sampling
• Chance factors
• IV-DV relationship varies across levels of another variable
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5 main categories of external validity
• Population Validity• Ecological Validity• Treatment Variation Validity• Outcome Validity• Time Validity
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Population Validity
• The extent to which the results of a study can be generalized to the larger population.
• Target population: the population to which we want to generalize the results
• Accessible population: the population of research participants available to the investigator
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Ecological Validity• The extent to which the results of a study can be
generalized across settings or environmental conditions
• Which research setting receives the most criticism here?– laboratory
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Temporal Validity• The extent to which the results of an experiment can be
generalized across time
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Treatment Variation Validity
• The generalizability of results across variation of the treatment
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Outcome Validity
• The generalizability of results across different but related dependent variables.
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Balancing Internal and External Validity
• Inverse relationship
• The conditions that increase internal validity (control) decrease external validity