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Chapter 6

# PSY201 Chapter 6 Correlation

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University of Toronto St. George

Psychology

PSY201H1

Kristie Dukewich

Fall

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Chapter 6 Correlation
- Correlation coefficient expresses the degree and direction of the relationship
- The direction of the relationship refers to whether the relationship is positive or negative
- The degree of the relationship refers to the strength of the relationship
- The direction and degree of the correlation coefficient must be independent of the differences in
units and scaling that exist between two variables
- Perfect relationship
- The same value of X always leads to the same value of Y
- The same value of Y always leads to the same value of X
- Imperfect relationship
- Prediction is approximate
- The same value of X doesn’t always lead to the same value of Y
- On average, Y changes systematically with X
- Predicting Y with better with the knowledge of X than without it
- Zero relationship
- The knowledge of X does not aid in predicting Y
- Linear correlation coefficient
- Pearson r is a measure of the extent to which paired scores occupy the same or
opposite positions within each of their distributions
- Pearson r can be interpreted in terms of the variability of Y accounted for by X
- In absence of a relationship between X and Y, the overall mean is the best
predictor of Y
- Minimizes prediction errors because the sum of the squared deviations
from the mean is a minimum
- When there is a relationship between X and Y, we use the line to predict Y
- Pearson (r) = both variables a

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