Comparing Variances Question Help

• Nov 8th 2011, 03:50 PM
youngb11
Comparing Variances Question Help
The McBurger company's management is interested in whether there is a difference in the standard deviation in services times for customers who use the drive-through window versus those who go inside to the service counter. A sample of \$\displaystyle 13\$ drive-through customers and a sample of \$\displaystyle 9\$ inside-counter customers were selected. The time (minutes) it took for each customer to be served was recorded. The following statistics are computed:
\$\displaystyle Drive-through: mean = 4.5, s = 2.0\$
\$\displaystyle Insider-counter: mean = 4.0, s = 1.2\$

Based on a significance level of \$\displaystyle 0.10\$, determine if there is a difference in the standard deviation in service time.

I'm assuming null hypothesis is var(drivethrough)/var(insider) = 1 and alternative hypothesis is var(drivethrough)/var(insider) /= 1, but I'm not sure of what to do after this. If anyone could post the steps I'll try to follow along, thanks!
• Nov 8th 2011, 07:50 PM
CaptainBlack
Re: Comparing Variances Question Help
Quote:

Originally Posted by youngb11
The McBurger company's management is interested in whether there is a difference in the standard deviation in services times for customers who use the drive-through window versus those who go inside to the service counter. A sample of \$\displaystyle 13\$ drive-through customers and a sample of \$\displaystyle 9\$ inside-counter customers were selected. The time (minutes) it took for each customer to be served was recorded. The following statistics are computed:
\$\displaystyle Drive-through: mean = 4.5, s = 2.0\$
\$\displaystyle Insider-counter: mean = 4.0, s = 1.2\$

Based on a significance level of \$\displaystyle 0.10\$, determine if there is a difference in the standard deviation in service time.

I'm assuming null hypothesis is var(drivethrough)/var(insider) = 1 and alternative hypothesis is var(drivethrough)/var(insider) /= 1, but I'm not sure of what to do after this. If anyone could post the steps I'll try to follow along, thanks!

F or variance ratio test.

1.3.5.9. F-Test for Equality of Two Standard Deviations

CB