a. Produce a scatter plot depicting the relationship between the life expectancy of women and men — bit good news for male students American have closed gap with span
Mathematics & StatisticsGeneralWorked Solution
In a bit of good news for male students, American men have closed the gap with women on life span, according to a USA Today article. Male life expectancy attained a record 75.2 years, and women’s reached 80.4. The National Center for Health Statistics provided the data given in the file titled Life.
a. Produce a scatter plot depicting the relationship between the life expectancy of women and men.
b. Determine the order of the polynomial that is represented on the scatter plot obtained in part a. Produce the estimated regression equation that represents this relationship.
c. Determine if women’s average life expectancy can be used in a second-order polynomial to predict the average life expectancy of men. Use a significance level of 0.05.
d. Use the estimated regression equation computed in part b to predict the average length of life of men when women’s length of life equals 100. What does this tell you about the wisdom (or lack thereof) of extrapolation in regression models?
SOLUTION
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a.
b. There appears to be one curve in the sample data. Therefore, a second-order polynomial seems to be the correct model.
SUMMARY OUTPUT
SUMMARY OUTPUT
Regression Statistics
Regression Statistics
Multiple R
0.9940
R Square
0.9880
Adjusted R Square
0.9871
Standard Error
0.2659
Observations
28
ANOVA
df
SS
MS
F
Significance F
Regression
2
145.6974
72.8487
1030.737
9.58492E-25
Residual
25
1.7669
0.0707
Total
27
147.4643
Coefficients
Standard Error
t Stat
P-value
Lower 95%
Upper 95%
Intercept
758.0664
56.5385
13.4080
6.43E-13
641.6232
874.5095
Women
-19.2549
1.4901
-12.9221
1.45E-12
-22.3238
-16.1861
Women Sq
0.1339
0.0098
13.6548
4.29E-13
0.1137
0.1541
The regression equation is:
Men = 758.0664 – 19.2549Women + 0.1339Women Sq
c. Since F = 1030.737 > 3.3852(Critical F with 2 and 25 df), we reject HO. There is sufficient evidence to conclude that women’s average life expectancy can be used in a second-order polynomial to predict the average life expectancy of men.
d. The predicted value is = 758.0664 – 19.2549(100) + 0.1339(100)2 = 171.58. Such an answer has little or no validity. An examination of the past data indicates that the average length of life of women has always been larger than that for man. This is an example of how unwise it is to extrapolate when using regression models.