An environmental research firm wants to estimate the proportion of cars in Jacks
ID: 2959578 • Letter: A
Question
An environmental research firm wants to estimate the proportion of cars in Jackson County Missouri that would be considered SUV's. Using the county's vehicle registration records they randomly select 250 vehicles. From that list they determined that 99 of them were SUV's.
Note: Report your answers to 4 decimal places.
Find the standard error of the sample proportion in this situation. 1
From this data we see that we are 95% confident that the true proportion of SUVs in Jackson County Missouri is between 2 and 3.
Explanation / Answer
The standard error for proportion is a measure of the spread of the distribution. For example in this case 99 out of n=250 vehicles means p= 99/250=39.6% of the vehicles are SUVs. SEprop = sqrt [(p)(1-p) / n ] SEprop = sqrt(.396*.604/250) =3.09%