Chapter 8 – Lecture 6
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Transcript of Chapter 8 – Lecture 6
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Chapter 8 – Lecture 6
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Hypothesis Question
Initial Idea(0ften Vague)
Initial Observations Search Existing Lit.
Statement of the problem
Operational definition of IV & DVResearch Hypothesis
“If” “Then”
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Correlation: there is a significant correlation (+/-)
between A & BDifferential (quasi):
there is a significant differencebetween A & B
Research Hypotheses
Experimental:Variable A will significantly affect
variable B
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Design experiment to test your hypothesis
Test the Null Hypothesis
“Statistical Hypothesis”
Alpha (0.05) 5% chance of differences btw groups due to chance (not a real difference)
5 times in 100 that difference is due to chance
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is all about control- environment - undesirable and irrelevant factors could creep into your experiment and affect your
results These factors are bad “threatens” validity of
results
It is important to understand these threats when designing an experiment so you can try
and avoid them
“9 Evil Threats”
Experimentation (Hypothesis Testing) Threats to Validity
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Are you measuring what you say you are measuring?
METHODOLOGY! Methodological Soundness
1)Anticipate potential threats to validity2)Create procedures to eliminate or reduce
threats
Validity
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Types of Validity
Statistical: accuracy of the conclusion drawn from a statistical test
Construct: how well the results support the theory or construct (internal condition of exp)
External: extent to which the results generalize (ecological validity)
Internal: your study demonstrates that the experiment was the sole cause for a change in the dependent variable – vs other factors (threats) not related to the experiment
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Types of Validity
Statistical: accuracy of the conclusion drawn from a statistical test
Testing the Null Hypothesis (is the differencechance variation or the IV)
Threats (1) measure used to measure DV is not reliable (2) violation of underlying statistical tests “assumptions” normality & homogeneity of variance
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Types of Validity
Construct: how well the results support the theory or construct
Hypothesis tested is gathered from theoreticalideas
Threats (1) begin with a weak theory (2) rival theories not carefully ruled out
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Types of Validity
External: generalization
Major Threat: NO random assignment
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Types of Validity
Internal: demonstration of causality
Was it what you did that made the DVchange or was it something else???
Did “A” cause “B”
9 Evil Threats to Internal Validity
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Changes to DV due to:Historical Event Ex: September 11th may have an effect on a study of patriotic behavior in college undergraduates
Pre TX TX Post TX
Compare ScoresSingle group pretest, Posttest Design
1. History
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Changes to DV due to: •natural processes in subjects•happen as a function of time•not as a function of the experiment
EX: aging, getting hungry, thirsty, more tired, etc. Ex: filling out a 500-item questionnaire…
- get tired - difficulty concentrating on answering
items- answers to items later in the test may be
different from previous items, even if the items are similar
2. Maturation
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Changes to DV due to: some aspect of a measurement instrument or scale, or some change in an observer or scorer
Ex: an observer of children’s play behavior- more proficient over time affecting
observation scores
Ex: equipment- measure RT becomes less and less exact due
to mechanical breakdown
3. Instrumentation
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Changes to DV due to: taking a pre-test which may affect scores on the post-test Ex: IQ test scores
- 3-5 points higher the second time - Reading test
4. Testing
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Changes to DV due to: participants are selected because their scores
on a measure are extreme (either high or low)…they will tend to be less extreme on a second testing (scores regress toward the mean some) Ex: Top 10% of a class – pretest shows they are above average….upon post test the change in score may not truly be due to your IV but due to the students score regressing toward the mean
5. Regression to the Mean
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Changes to DV due to: groups being compared are not equivalent before manipulation begins Ex: comparing students identified by teachers as ‘extremely motivated’ vs control group
- Recruited: $20 each- undesired effect of increasing motivation
6. Selection
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Changes to DV due to: loosing subjects can be death or not
- you lose participants for Exp. or control groups for different reasons and/or you lose different
numbers of participants in each group Ex: A clinical psychologist loses 40% of her Exp. Group but only 5% of the control group; the reason was because the “confrontation therapy” for the experimental group made clients too anxious to finish up treatment
7. Mortality
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Changes to DV due to: experimental groups communicating with each other – may give away the procedures …one group affects the other Ex: Dr. Suter’s experiment…one student tells another student what the experiment was about (contract effect..cow picture)…later the other student goes into the experiment knowing what is expected
8. Diffusion of TX
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Changes to DV due to: the order in which the subjectsreceive treatments (repeated measures..within subs)…carry over effects
Example: drugs…reading tests
9. Sequence Effects
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Subject effects: when people know they are being observed
Changes to DV due to: demand characteristic cues given to subjects on how to behave in experiment(unintentional) Ex: placebo effect
Also – threats to validity
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How to control all these threats
1. General control procedures2. Control over subject and experimenter effects3. Control through participant selection and assignment4. Control through specific experimental design
Chapter 9
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Preparation of setting – laboratory
Response Measurement - careful selection preparation of the instruments used to measure DV
Replication – “pilot data” 1. General control procedures
Single & double blind procedures Automation: reduce experimenter/subject contact (tape recording etc) Multiple observers:interrater reliability Using deception: obscure the true hypothesis (vodka)
2. Control over subject & Experimenter effects
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Random samplingSubject Assignment – random free random assigment (use random number table) matched random assigment – (age, weight)
3. Control through subject selection & assignment
Simple Pretest-posttest design Pretest-posttest , control group design
4. Control over experimenter design