Question

Police stops ~ The Minneapolis Police Department records data on all traffic stops made by their police officers such as race, gender, reason, citation issued, etc. The chief of police wants to collect a random sample of traffic stops.

The chief of police wants to estimate the actual proportion of drivers who are stopped that are female.

To calculate the required sample size, what value of p* should we use in the formula below to calculate a 90% confidence interval within 3.02 percentage points? Give exact answer as a decimal.

n=p*(1−p*)(z*ME)2

Answer 1

Solution,

Given that,

=  1 - = 0.5 ( no prior estimate )

margin of error = E = 0.0302

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05  = 1.645

sample size = n = (Z / 2 / E )2 * * (1 - )

= (1.645 / 0.0302)2 * 0.5 * 0.5

= 741.75

sample size = n = 742