Question

In: Statistics and Probability

Here is data with y as the response variable. x y 57.8 47.7 65.3 42.7 61...

Here is data with y as the response variable. x y 57.8 47.7 65.3 42.7 61 30.8 54.5 26.4 -70.7 -338.8 63 45.7 38.9 -46.1 70.2 35.5 Make a scatter plot of this data. Which point is an outlier? Enter as an ordered pair. For example (a,b) - with parenthesis. Find the regression equation for the data set without the outlier. Enter as an equation of the form y = a + b x . Rounded to three decimal places. Do not include the hat in y-hat. Find the regression equation for the data set with the outlier. Enter as an equation of the form y = a + b x . Rounded to three decimal places. Do not include the hat in y-hat. Is this outlier an influential point? No, the outlier does not appear to be an influential point. Yes, the outlier appears to be an influential point.

Solutions

Expert Solution

Scatter plot:

outlier = (-70.7, -338.8)

----------------------

Without outlier:

X Y XY
57.8 47.7 2757.06 3340.84 2275.29
65.3 42.7 2788.31 4264.09 1823.29
61 30.8 1878.8 3721 948.64
54.5 26.4 1438.8 2970.25 696.96
63 45.7 2879.1 3969 2088.49
38.9 -46.1 -1793.29 1513.21 2125.21
70.2 35.5 2492.1 4928.04 1260.25
Ʃx = 410.7
Ʃy = 182.7
Ʃxy = 12440.88
Ʃx² = 24706.43
Ʃy² = 11218.13
Sample size, n = 7
x̅ = Ʃx/n = 410.7/7 = 58.6714286
y̅ = Ʃy/n = 182.7/7 = 26.1
SSxx = Ʃx² - (Ʃx)²/n = 24706.43 - (410.7)²/7 = 610.074286
SSyy = Ʃy² - (Ʃy)²/n = 11218.13 - (182.7)²/7 = 6449.66
SSxy = Ʃxy - (Ʃx)(Ʃy)/n = 12440.88 - (410.7)(182.7)/7 = 1721.61

Slope, b = SSxy/SSxx = 1721.61/610.07429 = 2.8219678

y-intercept, a = y̅ -b* x̅ = 26.1 - (2.82197)*58.67143 = -139.4689

Regression equation :

y = -139.469 + (2.822) x

--------------------------------------

With outlier:

X Y XY
57.8 47.7 2757.06 3340.84 2275.29
65.3 42.7 2788.31 4264.09 1823.29
61 30.8 1878.8 3721 948.64
54.5 26.4 1438.8 2970.25 696.96
-70.7 -338.8 23953.16 4998.49 114785.44
63 45.7 2879.1 3969 2088.49
38.9 -46.1 -1793.29 1513.21 2125.21
70.2 35.5 2492.1 4928.04 1260.25
Ʃx = 340
Ʃy = -156.1
Ʃxy = 36394.04
Ʃx² = 29704.92
Ʃy² = 126003.57
Sample size, n = 8
x̅ = Ʃx/n = 340/8 = 42.5
y̅ = Ʃy/n = -156.1/8 = -19.5125
SSxx = Ʃx² - (Ʃx)²/n = 29704.92 - (340)²/8 = 15254.92
SSyy = Ʃy² - (Ʃy)²/n = 126003.57 - (-156.1)²/8 = 122957.669
SSxy = Ʃxy - (Ʃx)(Ʃy)/n = 36394.04 - (340)(-156.1)/8 = 43028.29

Slope, b = SSxy/SSxx = 43028.29/15254.92 = 2.8206172

y-intercept, a = y̅ -b* x̅ = -19.5125 - (2.82062)*42.5 = -139.3887

Regression equation :

y = -139.389 + (2.821) x

------------------------

No, the outlier does not appear to be an influential point.


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