# Statistics proportion/confidence interval question?

An oil company in Houston is looking for a hardware

supplier for drilling machinery. They want to find

whether Supplier 1 is better than Supplier 2. Let p1

and p2 be the proportion of defective items from Supplier 1 and 2 respectively. Smaller proportion of defective item is better. They want to test (p1 − p2) ≥ 0 vs

(p1 − p2) < 0. If the 95% confidence interval is given

by (-0.06, 0.15) which of the following is correct?

A. p-val > 0.05, so there is significant evidence to support the statement, ”Supplier 1 had similar proportion of defective item as Supplier 2”.

B. p-val > 0.05, so there is significant evidence to

support the statement, ”Supplier 1 had more defective items than 2”.

C. p-val < 0.05, so there is significant evidence to support the statement, ”Supplier 1 had less defective

items than Supplier 2”.

D. A & B

E. None of the above

I know the correct answer is D but can someone explain why?

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