Chapter 12 Correlational Designs Power Point Slides by
Chapter 12 Correlational Designs Power Point Slides by Ronald J. Shope in collaboration with John W. Creswell
Key Ideas • Purpose and use of correlational designs • Types of correlational designs • Key characteristics of correlational designs • Procedures used in correlational studies Educational Research 2 e: Creswell
What is correlational research? • In correlational research designs, investigators use the correlation statistical test to describe and measure the degree of association (or relationship) between two or more variables or sets of scores. Educational Research 2 e: Creswell
When do you use correlational designs? • To examine the relationship between two or more variables • To predict an outcome – Co-vary – Use one variable to predict the score on one variable using knowledge about the other variable • Statistic that expresses linear relationships is the Product-Moment Correlation Coefficient Educational Research 2 e: Creswell
Types of correlational designs: Prediction designs • Predictor Variable: a variable that is used to make a forecast about an outcome in the correlational study. • Criterion Variable: the outcome being predicted • “Prediction” usually is a word in the title • Predictor variables usually measured at one point in time and the criterion variable at a later point in time. • Purpose is to forecast future performance Educational Research 2 e: Creswell
Displays of scores in a Scatterplot Hours of Internet Depression use scores per week from 15 -45 Depression scores Y=D. V. 50 - 40 30 20 + 10 5 Educational Research 2 e: Creswell + M M - 10 15 20 Hours of Internet Use X=I. V.
Displays of scores in a correlation matrix 1 1. School satisfaction - 2. Extra-curricular activities -. 33** 3. Friendship . 24 2 -. 03 3 - 4 5 - 4. Self-esteem -. 15 . 65**. 24* 5. Pride in school -. 09 -. 02 . 49**. 16 - 6. Self-awareness . 29** -. 02 . 39**. 03 . 22 Educational Research 2 e: Creswell 6 -
Associations between two scores • Direction (positive or negative) • Form (linear or non-linear) • Degree and strength (size of coefficient) Educational Research 2 e: Creswell
Association Between Two Scores Linear and non-linear patterns A. Positive Linear (r=+. 75) B. Negative Linear (r=-. 68) C. No Correlation (r=. 00) Educational Research 2 e: Creswell
Linear and non-linear patterns D. Curvilinear E. Curvilinear F. Curvilinear Educational Research 2 e: Creswell
Association Between Two Scores Degree and strength of association • . 20–. 35: When correlations range from. 20 to. 35, there is only a slight relationship • . 35–. 65: When correlations are above. 35, they are useful for limited prediction. • . 66–. 85: When correlations fall into this range, good prediction can result from one variable to the other. Coefficients in this range would be considered very good. • . 86 and above: Correlations in this range are typically achieved for studies of construct validity or test-retest reliability. Educational Research 2 e: Creswell
Simple Regression Line 50 41 40 Depression Scores 30 Slope 20 10 Intercept 5 10 14 15 Hours of Internet Use Per Week Educational Research 2 e: Creswell 20
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