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Correlation Indicates the relationship between two dependent variables (x and y) Symbol: r (Pearson correlation coefficient) -1< r < 1. Positive Correlation As value of variable X increases, value of variable Y increases. Strong Positive Corr. r = .80. - PowerPoint PPT Presentation
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Correlation
Indicates the relationship between two dependent variables (x and y)
Symbol: r (Pearson correlation coefficient)
-1< r < 1
Strong positive correlation:
- low variability of the data
- one variable acts as a good predictor of the second variable.
Variables measured on different scales
e.g. Height and weight
Correlation formula converts the scores into z-score to make them comparable
r
n XY X Y
n X X n Y Y
2 2 2 2
Multiply each value of X by its corresponding Y.
Add the products.
Multiply sum by n
Quiz One Quiz Four
(X) (Y) Y2
28 30.5 930.25
28 29.5 870.25
30 39 1521
29 36.5 1332.25
21 30.5 930.25
Y2 = 5584
Quiz One Quiz Four
(X) (Y) (X)(Y)
28 30.5 854
28 29.5 826
30 39 1170
29 36.5 1058.5
21 30.5 640.5
XY = 4549
# of absences test grade 8 64 35 1225 0 0 48 2304 3 9 43 1849 2 4 41 1681 5 25 39 1521 6 36 36 1296 X2= 138 Y2 = 9876