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Correlation Research

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

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Correlation Research

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  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

  2. 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

  3. 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

  4. 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

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

  6. Non-linear relationships

  7. Outliers

  8. Range restriction

  9. 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: • A ____________ (chance) relationship e.g., tobacco industry states no direct causal link between smoking and lung cancer in humans, only correlational data • _________________ - A causes B, or B causes A e.g. Violent TV and children’s aggression • ______________ - anther variable influences both A and B e.g., Aggressive parents or social skills may influence both preference for violent TV and aggressive behavior

  10. 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

  11. 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.

  12. 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?

  13. Time 2 Time 2 Time 1 Time 1 .03 .03 A A A A .01 .35 .25 .30 .30 .25 .32 .05 B B B B .25 .25 Helping determine causality:_____________________correlation • Measures two variables at two points in time A at Time 1 correlated with B at Time 2. Supports view that A affects B B at Time 1 correlated with A at Time 2. Supports view that B affects A

  14. Helping determine causality:Partial-correlations • 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. .32 .02 A B .43 .52 C

  15. Helping determine causality:Multivariate-correlations • _______________ 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

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