Research into the relationship between hours of study and grades show widely different conclusions. A recent survey of graduates who wrote the Graduate Management Admissions Test (GMAT) had the following results.
Hours Studied Average Score
(Midpoint)
64 350
72 450
79 550
106 650
99 750
The Excel output for this regression is as following
SUMMART OUTPUT
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Regression Statistics
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Multiple R 0.919958
R Square 0.846322
Adjusted R Square 0.795097
Standard Error 71.57225
Observations 5
Anova
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DF SS MS F Sign. F
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84632.2 84632.2 16.521 0.0268
Regression. 1 4 4 4 6
15367.7 5112.58
Residual 3 6 7
Total 4 100000
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Coefficient Standard Lower Upper
s Error t Stat P-Value 95% 95%
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171.192 0.4921 411.24
Intercept -133.568 8 -0.78022 6 -678.38% 4
0.0268
X Variable 1 8.137715 2.00207 xxxxxx 6 1.7662 14.509
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a) How accurate is this regression at predicting GMAT scores base on hours studied? Explain.
b) What is the regression equation for this relationship?
c) Use the regression equation to predict the average score for each category of hours studies.
d) Calculate the t statistic to determine approximately how “significant” this regression is (note that the t may be greater than or less than the value from the t table).
Q1: From ANOVA table p- value = 0.0268
Since p-value is less than 0.05,we reject the null hypothesis and can say that the regression model is significant to predict the GMAT scores.
Coefficient of determination, r2 = 0.8463
So about 84.63% variation in the response variable GMAT score explained by predictor variable hours studied.
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Q2: Regression equation :
ŷ = -133.5681 + (8.1377) x
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Q3:
X | Y | Predicted score, ŷ |
64 | 350 | -133.5681 + (8.1377) * 64 = 387.2457 |
72 | 450 | -133.5681 + (8.1377) * 72 = 452.3474 |
79 | 550 | -133.5681 + (8.1377) * 79 = 509.3114 |
106 | 650 | -133.5681 + (8.1377) * 106 = 729.0297 |
99 | 750 | -133.5681 + (8.1377) * 99 = 672.0657 |
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Q4: Test statistic:
t = b /se(b1) = 8.137715/ 2.00207 = 4.0647
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