18)

Lead Toxicity in Drinking Water The US Environmental Protection Agency has set the action level for lead contamination of drinking water at 15 ppb (parts per billion).¹

Samples are regularly tested to ensure that mean lead contamination is not above this level.

Suppose we are testing:

H0:=15

Ha:>15

and we have created a randomization distribution from our sample. Two possible sample means are shown:

A:x=19.7 B:x=15.8

¹www.atsdr.cdc.gov

(a) Which sample mean, A or B, will be closer to the center of the randomization distribution?

A

B

(b) Which sample mean, A or B, will be farther out in the tail of the randomization distribution?

A

B

e of the new entries may impact the last attempt grading.

Your answer is incorrect.

(c) Which sample mean, A or B, will provide the stronger evidence against H₀ and in support of H_a?

A

B

(d) Explain in the context of lead contamination what it means to "provide evidence against

H₀ and in support of H_a."

We found evidence that the mean lead contamination is equal to 15 ppb.

We have evidence that the sample had a mean lead contamination greater than 15.

We have evidence that mean lead contamination in this water is greater than 15 ppb.

We do not have enough evidence to make any kind of claim about lead contamination.