Correlation and Experimentation AP Psychology

 What does it mean when we say two things are correlated?  Why do correlations permit prediction but not explanation?  Correlation coefficient  Measures the relationship between two variables  How well one variable predicts the other  r  Closer to 1 = more strongly related  + correlation means variables move in the same direction  - correlation means variables move in different dorections Correlation

 Graphs of two variables that may or may not be related Scatterplots

Are these Correlated? Draw Best Fit Lines

 Some correlations (What’s the causal factor?)  Ice Cream Consumption Positively correlates with violent crime  # of years of marriage correlates with amount of gray hair or amount of hair loss  Problematic Causal Arrows  Low Self esteem depression  Parental love and acceptance positive behavior  Correlation indicates the POSSIBILITY of a causal relationship but does not prove that one exists Correlation and Causation

 A perceived nonexistent correlation  We are more likely to recall observations that confirm the correlation (Troiler and Hamilton1986)  More babies are born when the moon Is full  Couples who adopt become more likely to conceive  Sugar makes children hyper  Arthritic patients can predict barometric changes (Redelmeier and Trevsky 1996)  Sensitivity to dramatic or unusual events  When we notice random coincidences, we forget that they are random Illusory Correlations

 Random sequences don’t often look random  People expect lack of pattern in random sequences (Kahneman and Tversky 1972)  People favor randomness in picking lottery numbers, even though repeated numbers are just as likely (Holtgraves and Skeel 1992)  Brains LOVE patterns  We are startled by coincidences and tend to remember them and think something special about them  (The called shot?) Perceiving order in Random Events

 How do experiments clarify or reveal cause and effect relationships?  What is random assignment, and why is it important?  Experiments isolate variables and control for other factors  Turning correlation into causation  Breastfed infants have higher iq’s (Angelson et al 2001, Gale and Martin 1996, Johnson et al 1996, Luca et al 1996, Mortensen et al 2002, Quinn et al 2001)  Smarter mothers tend to breastfeed?  Mother’s milk helps brain development?  Correlation must be controlled for iq of mother, maternal age, and maternal education  How to isolate cause and effect  Manipulate the factors of interest  Control for other factors  Randomly assign the control and the test groups (Lucas 1998 breastmilk study) Experimentation

 Illusory correlations can exist for treatment protocols  Vitamin C for a cold (MY cold got better!)  Subliminal tape before exam (I passed = it worked!)  Antibiotics for sinus infections  Controlling for variables in experimental treatments  Blind studies: patient does not know which treatment (if any) he/she is getting  Double blind studies: patient does not know which treatment he/she is receiving and person administering treatment does not know which treatment he/she is administering  Placebo effect: sometimes people get better even if they are in the control group (Kirsh and Sapirstein 1998) Evaluating Therapies

 Experimental condition: people receiving the treatment  Control condition: people receiving the placebo  Random assignment  Each participant has an equal opportunity to be in each group  Groups should be statistically identical  Treatment study designs  Hormone replacement therapy increases health risks (Love 2002)  Viagra Study (Goldstein et al 1998)  Independent Variable: variable that is manipulated (drug or placebo)  Dependent Variable: measurable outcome researcher is trying to manipulate  Operational definitions provide both a definition and a means of measurement for each variable Experimental Design

 Can Subliminal Tapes improve your life?  The urban myth of the subliminal popcorn ad  Multitude of subliminal messaging products that claim to feed you positive reinforcements so that you can succeed in school, lose weight, quit smoking, or feel good about yourself.  1991 study by Greenwald, et al  Students assigned to listen to memory improvement tapes every day for 5 weeks  Half listened to “self-esteem,” half listened to memory  Pre and post tested on actual self esteem and memory  Pre and post tested on perception of self esteem and memory  No change on actual test, big changes on perceptual test  General public does not understand importance of blind studies (Miller and Pifer 1996) The Case of the Subliminal Tapes

 Exit Ticket  Why is experimental design sometimes interpreted as superior to other forms of psychological study?  Why is it important to have a control group?  Homework  Define each of the following and provide an example  correlation coefficient  scatterplot  illusory correlation  Experiment  Double-blind procedure  Placebo effect  Experimental condition  Control condition  Random assignment  Independent variable  Dependent variable  How would you design an experiment to test whether or not doing crosswords improved a person’s verbal skills?  How would you design an experiment to test whether or not attractive people are more likely to be hired than unattractive people? Exit Ticket and Homework