In: Statistics and Probability
Experts have predicted that approximately 1 in 12 tractor-trailer units will be involved in an accident this year. One reason for this is that 1 in 3 tractor-trailer units has an imminently hazardous mechanical condition, probably related to the braking systems on the vehicle.
1. If you wanted to calculate a 99% confidence interval that is no wider than 0.06, how many tractor-trailers would you need to sample?
Solution,
Given that,
= 1 - = 0.5
margin of error = E = 0.06
At 99% confidence level
= 1 - 99%
= 1 - 0.99 =0.01
/2
= 0.005
Z/2
= Z0.005 = 2.576
sample size = n = (Z / 2 / E )2 * * (1 - )
= (2.576 / 0.06)2 * 0.5 * 0.5
= 460.81
sample size = n = 461