Question

Suppose a legislator is deciding whether they should put in the effort to draft a bill. The legislator only wants to do this if they are convinced that a majority of their consituents support the bill. The legislator runs a poll of 1,000 constituents, and will be convinced that a majority of their constituents support the bill if the lower bound of the 95% confidence interval for the probability that a constituent supports the bill is greater than 0.50. 550 out of the 1,000 constituents polled indicate support for the bill. Will the legislator put in the effort to draft the bill? (Possible answers are yes or no).

Answer 1

Solution:

We are given that: The legislator runs a poll of 1,000 constituents, and will be convinced that a majority of their constituents support the bill if the lower bound of the 95% confidence interval for the probability that a constituent supports the bill is greater than 0.50.

550 out of the 1,000 constituents polled indicate support for the bill.

Thus x = 550 and n =1000

Thus sample proportion of people who support for the bill is:

Formula for confidence interval is:

where

Find z_c value for c=95% confidence level.

Find Area = ( 1 + c ) / 2 = ( 1 + 0.95) /2 = 1.95 / 2 = 0.9750

Look in z table for Area = 0.9750 or its closest area and find z value.

Area = 0.9750 corresponds to 1.9 and 0.06 , thus z critical value = 1.96

That is : Z_c = 1.96

Thus

Thus

Thus the 95% confidence interval for the population proportion that a constituent supports the bill isin between ( 0.5192 , 0.5808).

Will the legislator put in the effort to draft the bill?

Yes, Since this confidence interval is greater than 0.50.