In: Statistics and Probability
A company keeps extensive records on its new salespeople on the
premise that sales should increase with experience. The months on
the job x and monthly sales y from a random sample of seven new
salespeople resulted in the regression output shown below.
Note that x = 5.8571
Calculate a 95% confidence interval for the mean monthly sales of
all employees that have worked at the company for x = 6 months
(round to 2 decimal places).
lower bound
upper bound
ANSWER::
Regression equation :
ŷ = -0.2462 + (1.3152) x
Predicted value of y at x = 6
ŷ = -0.2462 + (1.3152) * 6 = 7.645
Significance level, α = 0.05
Critical value, t_c = T.INV.2T(0.05, 5) = 2.5706
Standard error, se = 1.5770
Standard error of slope, s(b1) = 0.16192
95% Confidence interval :
Lower bound= ŷ - tc*se*√((1/n) + ((x-x̅)²/(se/s(b1)²)))
= 7.645 - 2.5706*1.577*√((1/7) + ((6 - 5.8571)²/(1.577/0.16192)²)) = 6.11
Upper bound = ŷ + tc*se*√((1/n) + ((x-x̅)²/(se/s(b1)²))
= 7.645 + 2.5706*1.577*√((1/7) + ((6 - 5.8571)²/(1.577/0.16192)²)) = 9.18
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