The US Department of Transportations National Highway Traffi

The U.S. Department of Transportation\'s National Highway Traffic Safely Administration reported that 77% of all fatally injured automobile drivers were intoxicated. A random sample of 27 records of automobile driver fatalities in Kit Carson County, Colorado, showed that 15 involved an intoxicated driver. Do these data indicate that the popuulation proportion of driver fatalities related to alcohol is less than 77% in Kit Carson County? Use alpha = 0.01.

Solution

A random sample of n=27 fatalities were recorded    

f=15 were found to involve intoxicated driver

sample proportion is p=f/n=15/27=.55   

Let population proportion be P

We need to test H0:P=.77 VS P<.77

Application of one sample proportion test yields the p value as .0002 i.e the data favours that population proportion is less than 77 %