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# Exam 5 Comprehensive Notes

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School
Ohio State University
Department
Psychology
Course
PSYCH 2220
Professor
All
Semester
Fall

Description
Psych Test 5 11/15/2012 Correlation: measures association, or relationship, between two variables Examples performance and speed grades and class attendance gpa and facebook friends Scatterplots Linear v nonlinear Positive v negative  Y­axis: Criterion  X­axis: Predictor Each data point represents a person Requirements for Pearson’s r Linear relationships Normally distributed variables Continuous variables Few, if any, outliers Correlation Coefficient Ranges from ­1 to +1 Direction +: variables change in same direction ­: variables change in opposite directions Size Absolute value closer to 1 means strong correlation Correlation Formula: looking at scatterplots, degree to which data points cluster around line of best fit Covariance: statistic representing degree to which two variables vary (or change) together correlation is a covariance of two variables  ∑ (x− x)(y − y) cov xy= N −1 2 2 ∑ (x− x) s = N −1 Standardized Covariance cov xy r = s s x y 2 x − (∑) x ∑ N s = N −1 Degrees of Freedom for Correlation df = N −2 Correlation Formula r =∑ x y N ∑ xy − ∑ y r = N  2 ∑ x) 2 ∑ y) ∑ x − N  y − N  Hypothesis Testing Specify hypotheses =H 0 ρ = 0 H 1ρ ≠ 0 Specify decision criteria Execution State conclusions Reject Ho: We can conclude that there is a significant relationship between age & post­surgical pain. Hypotheses aren’t about group means but about whether or not variables are related r = statistic;   p (rho)?= parameter Making scatterplots is helpful Correlation will always be two­tailed tests Coefficient of determination: proportion of variance variables have in common 2    0
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