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Correlations

Correlations. Correlational studies. What is a correlation? r, Pearson’s r Magnitude vs. sign vs. significance Negative vs. positive correlation. Example. Correlation<>Causation. Directional problem 3 rd variable problem. Examples—3 rd variable problem.

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Correlations

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  1. Correlations

  2. Correlational studies • What is a correlation? • r, Pearson’s r • Magnitude vs. sign vs. significance • Negative vs. positive correlation

  3. Example

  4. Correlation<>Causation • Directional problem • 3rd variable problem

  5. Examples—3rd variable problem • The more ice cream being sold, the more deaths by drowning. • People who eat more lobster tend to live longer. • College students who drink more alcohol tend to have poorer grades. • The more storks nesting on N. European rooftops, the more births 9 months later. • Cities with more churches also tend to have more crime. • Teenage boys who participated in Boy Scouts commit fewer street crimes. • http://www.tylervigen.com/spurious-correlations

  6. Headlines • Taller people more prone to cancer • Internet use in class leads to lower test scores • These 3 personality traits affect what you earn—but only after age 40 • Vegetarians are more depressed

  7. 3 things that can bias correlations • Truncated range • Outliers • Small n

  8. Scatterplots

  9. Cross-lagged correlations Opree, Buijzen, & Valkenburg, 2012

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