Sleeping and Happiness Hours slept (X) Happiness (Y) Pam 8 7 Jim 9 Dwight 5 4 Michael 6 Meredith You are interested in the relationship between hours slept and happiness. 1) Make a scatter plot 2) Guess the correlation 3) Guess and draw the location of the regression line
. . . . . r = .76
Remember this: Statistics Needed Need to find the best place to draw the regression line on a scatter plot Need to quantify the cluster of scores around this regression line (i.e., the correlation coefficient)
Regression allows us to predict! . . . . .
Straight Line Y = mX + b Where: Y and X are variables representing scores m = slope of the line (constant) b = intercept of the line with the Y axis (constant)
Excel Example
That’s nice but. . . . How do you figure out the best values to use for m and b ? First lets move into the language of regression
Straight Line Y = mX + b Where: Y and X are variables representing scores m = slope of the line (constant) b = intercept of the line with the Y axis (constant)
Regression Equation Y = a + bX Where: Y = value predicted from a particular X value a = point at which the regression line intersects the Y axis b = slope of the regression line X = X value for which you wish to predict a Y value
Practice Y = -7 + 2X What is the slope and the Y-intercept? Determine the value of Y for each X: X = 1, X = 3, X = 5, X = 10
Practice Y = -7 + 2X What is the slope and the Y-intercept? Determine the value of Y for each X: X = 1, X = 3, X = 5, X = 10 Y = -5, Y = -1, Y = 3, Y = 13
Finding a and b Uses the least squares method Minimizes Error Error = Y - Y (Y - Y)2 is minimized
. . . . .
. . . . . Error = Y - Y (Y - Y)2 is minimized Error = 1 Error = .5
Finding a and b Ingredients r value between the two variables Sy and Sx Mean of Y and X
b = b r = correlation between X and Y SY = standard deviation of Y SX = standard deviation of X
a a = Y - bX Y = mean of the Y scores b = regression coefficient computed previously X = mean of the X scores
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41 b =
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41 b = .88 1.50 1.41
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41 b = 1.5 a = Y - bX
Mean Y = 4.6; SY = 2.41 r = .88 Mean X = 3.0; SX = 1.41 b = 1.5 0.1 = 4.6 - (1.50)3.0
Regression Equation Y = a + bX Y = 0.1 + (1.5)X
Y = 0.1 + (1.5)X . . . . .
Y = 0.1 + (1.5)X X = 1; Y = 1.6 . . . . . .
Y = 0.1 + (1.5)X X = 5; Y = 7.60 . . . . . . .
Y = 0.1 + (1.5)X . . . . . . .