lecture5.ppt
- 1. Lecture Outline Introduction to experimental research Introduction to correlational research Three types of research validity Class Activity
- 2. Experimental Research Overview and Major Features An independent variable (IV) is manipulated A dependent variable(s) (DV) is measured Many basic experiments consist of two levels of the independent variable experimental group control group Control over extraneous variables holding constant randomizing effects A causal relationship between the independent and dependent variables can be established
- 3. Basic Goal of Experimental Design Manipulate possible values of the IV Observe behavioral changes as indexed by values of the DV
- 4. Basic Characteristics of Experimental Designs Subjects are randomly assigned to research groups A given participant must be equally likely to be assigned to any of the given groups Random number table Flip a coin In experimental designs, a causal relationship between the independent and dependent variables can be established
- 5. Independent Variable Differing values of the IV are called “levels” May vary quantitatively 10 mg day 20 mg day e.g. here are 2 levels of variable dosage May vary qualitatively Zoloft Imipramine Prozac e.g. here are 3 levels of the variable medication type
- 6. •An operational definition is a clearly defined set of procedures for measuring or manipulating the construct of interest. •The key to an acceptable operational definition is that the procedure is specified precisely enough to allow replication by others. Examples: quality of memory -- accuracy of recall in a certain task depression -- Beck Depression Inventory (survey) score arousal -- galvanic skin response (conductivity of the surface of the skin) Operational Definitions
- 7. She is a good car salesperson She: 1. Sells many cars 2. Points out + features 3. Is nice 4. Sells only good cars Verbal Statement Operational Definition Operational Definitions: Examples
- 8. Stress 1. Environment/Number of stressors a. Number negative Life events b. Number of Examinations 2. Self-report Measurable Nervous mood 3. Behavior a. number of fidgets/minute b. Psychophysiological responses elevated Verbal Statement Operational Definition Operational Definitions: Examples
- 9. Identify Key Experimental Features Social loafing refers to people’s tendency to slack on group tasks. In one study on social loafing college participants cheered alone, and in groups of 2, 4, or 6 ppl. They were told to cheer as loud as possible at specific times so researchers could determine how much noise people made in social settings. The amount of noise made by each participant dropped as group size increased. 1) What is the IV? 2) What is the DV? 3) Why is random assignment important here?
- 10. Correlational Research: Major Features No independent variables are manipulated Two or more variables are measured and a relationship established Correlational research does not show causality Don’t confuse statistics with research design Correlation coefficients ( a statistic) can be used in correlational or experimental research designs (although they are more commonly used in correlational designs)
- 11. Correlational Research 2 Variables Positive and Linear Negative and Linear
- 12. Example of Non-Linear Relationship Yerkes-Dodson Law Performance Arousal Better Worse Low High
- 13. Correlation Does Not Imply Causation Causality – must demonstrate that changes in one variable can only be due to influence of the other variable Directionality of Effect Problem Third Variable Problem
- 14. Directionality of Effect Problem X Y X Y X Y
- 15. X Y X Y Class Attendance Higher Grades Class Attendance Higher Grades Directionality of Effect Problem
- 16. X Y X Y Aggressive Behavior Viewing Violent TV Aggressive Behavior Viewing Violent TV Aggressive children may prefer violent programs or Violent programs may promote aggressive behavior Directionality of Effect Problem
- 17. Third Variable Problem X Y Z
- 18. Class Exercise Identify the third variable that influences both X and Y
- 19. Third Variable Problem Number of Churches Crime Rate +
- 21. Third Variable Problem Ice Cream Consumed Number of Drownings +
- 22. Measurement Considerations Variables should be measured accurately and consistently. Accuracy Validity Bathroom scale gives correct weight Consistency Reliability Bathroom scale gives same weight consistently
- 23. Evaluating Research: 3 Validities Validity How accurate is the information from our research? Three validities Construct validity Internal validity External validity
- 25. Construct Validity The degree to which the construct can be inferred from the operational definition of that construct Never one perfect operationalization Schacter and Singer (1962) Two-factor theory of emotion: Emotions require arousal and label Factor 1: AROUSAL Participants received epinephrine shots and either informed them of side-effects or not Factor 2: LABEL Participants around "euphoric" or "angry“ confederate
- 26. How Valid are These Manipulations? Euphoria Confederate shoots rubber bands, plays with hula hoops and crumples up paper and practices hook shots into wastebasket Anger Confederate complains about the injection, adds negative comments about the questionnaire they are filing out and ends up ripping up the questionnaire.
- 27. Simplified Results Euphoria Condition Anger Condition Informed of epinephrine effects Uninformed of epinephrine effects
- 28. Internal and External Validity Internal validity The extent to which the observed effect is caused only by the experimental treatment condition The ability to draw conclusions about a causal relationship from our data Experiments usually high in this External validity The extent to which the results can be applied to and across different persons, settings and times AKA generalizability Experiments often low in this
- 29. Generalizing From the Lab Setting Mundane realism The extent to which an experiment is similar to real-life situations Psychological realism The extent to which an experiment triggers relevant psychological and group processes Key point Lab experiments not automatically artificial When an experiment lacks mundane realism it may be very realistic in terms of psychological realism
- 30. Assess Internal & External Validity Does lighting affect productivity? Study 1: Give people a production task in a laboratory. The lab room is either bright or dim. Measure and compare their productivity (how quickly and accurately they perform the task). Study 2: Give employees in a well-lit office and those in a dim office a production task. Measure and compare their productivity (how quickly and accurately they perform the task).
- 31. The Tradeoff Real life situations High external validity Hard to rule out other explanations Low internal validity Lab settings High internal validity Often artificial and findings can’t be generalized Low external validity
- 32. Class Exercise Hypothesis and Operational Definition Exercise