1 Correlation Research Goal is to explore ______________ between variables Causal-comparative research: compare mean scores across groups. The “IV” is a __________ variable. e.g., compare salaries in those who complete and do not complete college Correlational research: analyze multiple scores ______ _____________. Collect two sets of data for each participant at one point in time. The “IV” is a quantitative variable. e.g., compare number of years of education to salary Neither approach yields ____________ information Both are non-experimental – no manipulation of an ___ Both used when researchers are _________ to experiment

3 2 Types of Variables ______________ variables (~IV)  allow prediction of some criterion variables e.g., SAT & college GPA e.g., TV & aggression _____________ variables (~DV)  the object of our research e.g., SAT & college GPA e.g., TV & aggression

4 Method Develop hypothesis or research question  e.g., What is the relationship between x and y? Select homogenous group Data collection  measures must be psychometrically sound Data analysis  correlational statistics (______________) - denotes strength of correlation, sign +/- indicates direction  Graphed on a ______________  Correlation coefficients range from ___________ Threats to Internal validity  no huge concerns- not identifying functional relationship Threats to External validity  _______________________ of sample

Positive correlation As one variable goes up, the other variable goes ___, e.g., class attendance and grades Negative correlation As one variable goes up, the other goes _____, e.g., alcohol consumption and grades

7 Factors Affecting Coefficients 1. ___________________  a curvilinear relationship would result in a lower coefficient  Correlation-coefficients only useful for linear relationships 2. Outliers  _____________ scores  May inflate or deflate r values 3. Restricted ___________  Reduces correlation  e.g., GPA & SAT

8 Non-linear relationships

9 Outliers

10 Range restriction

11 Correlation vs. Causation If no correlational relationship, no causation Strong relationship might suggest a causal relationship, but A strong relationship could also be the result of: 1. A ____________ (chance) relationship e.g., tobacco industry states no direct causal link between smoking and lung cancer in humans, only correlational data 2. _________________ - A causes B, or B causes A e.g. Violent TV and children’s aggression 3. ______________ - anther variable influences both A and B e.g., Aggressive parents or social skills may influence both preference for violent TV and aggressive behavior

12 Describe some problems of determining causality. Amount of soda consumed each day is correlated with obesity level Height of children is correlated with popularity Number of hours of sleep per night is correlated with depression

13 Problem with correlations: The Case Against Bread More than 98% of convicted felons are bread users. Fully half of all children who grow up in bread consuming households score below average on standardized tests. In the 18th century, when virtually all bread was baked in the home, the average life expectancy was less than 50 years; infant mortality rates were unacceptably high; many women died in childbirth; and diseases such as typhoid, yellow fever, and influenza ravaged whole nations. More than 90% of all violent crimes are committed within 24 hours of eating bread. Primitive tribal societies that have no bread exhibit a low incidence of cancer, Alzheimer's, and Parkinson's disease.

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15 Research Design: You are interested in the relationship between exercise and stress. How would you design a study to investigate this relationship using: A causal comparative design? A correlational study? Why would you choose one over the other?

Helping determine causality: _____________________correlation Measures two variables at two points in time B at Time 1 correlated with A at Time 2. Supports view that B affects A A at Time 1 correlated with B at Time 2. Supports view that A affects B A A BB Time 1 Time 2 A A BB Time 1 Time 2

17 Allows you to help rule out a _____ variable as a cause.  Relationship between stress and alcohol consumption – also measure socioeconomic status to control or “__________” the influence of a third variable. Helping determine causality: Partial-correlations A B C

18 _______________ correlation - Correlation between two variables  e.g., relation between stress and alcohol consumption _________________ correlation - Correlation between multiple predictor and one criterion variables  e.g., relation between stress, socio-economic status, family history and alcohol consumption  Also allows you to rule out or analyze the effects of many third variables Helping determine causality: Multivariate-correlations