Consists of a set of ordered pairs Indicates both the magnitude and direction of the relationship between variables Range is from -1.0 to +1.0 Correlation --- Basic Concepts

Fathers Height (in inches) Son’s Height * * * * * * * * * *

Consider these --- A correlation exists between: The total amount of losses in a fire and the number of firemen that were putting out the fire Cigarette smokers and lower GPAs The number of churches in a city and amount of alcohol consumed The amount of fat in diets and cancer rates

Good Poor False Rejections Correct Acceptances Correct Rejections False Acceptances Fail Pass Cut-off score Job Performance Test scores

X Computation of Standard Deviation & Variance x (EX/N) = 30 (Mean) EX = 150 Test Scores Deviation scores (scores minus the mean) x2x Squared deviation scores EX 2 = 1000 (Sum of the squared deviation scores) EX 2 /N = 200 (the variance or s 2 ) 200 = (standard deviation) s2s2 = standard deviation or s Mean of the sum of the squared deviation scores

Computational Formula for r X Y XY X Y  X = 15  Y = 25  XY = 83  X = 55  Y = 135 r = = = = = =.80 N  XY – (  X) (  Y) 5(83) – (15)(25)  [N  X – (  X) ][N  Y - (  Y) ]  [5(55) – (15) ][5(135) – (25) 415 –  (275 – 225)(675 – 625)  (50)(50)

Test Scores Job Performance * * * * * * * * * * Positive Correlation

Absenteeism (in hours) Job Performance * * * * * * * * * * Negative Correlation

Test Scores Job Performance * * * * * * * * ** ** * * Poor Good FailPass Correct Acceptances Correct Rejections False Acceptances Significant Correlation False Rejections

Test Scores Job Performance * * * * * * * * * * * * * No Correlation Poor Good FailPass False Rejections Correct Acceptances Correct Rejections False Acceptances

Test Scores Job Performance * * * * * * * * ** ** * * Poor Good FailPass Correct Acceptances Correct Rejections False Acceptances Significant Correlation False Rejections Effect of raising cutoff score?

Test Scores Job Performance * * * * * * * * ** ** * * Poor Good FailPass Correct Acceptances Correct Rejections False Acceptances Significant Correlation False Rejections Effect of lowering cutoff score?