A study was conducted to evaluate the contaminants in fish caught in the Housato

Question

A study was conducted to evaluate the contaminants in fish caught in the Housatonic River. Independent samples of Smallmouth bass were obtained from two different locations (Bull’s Bridge and Lake Zoar) and each fish was tested for PCBs (polychloridnate biphenyls). PCBs are measured in parts per million (ppm). Construct and interpret a 95% confidence interval for the difference in the mean PCB levels for the two locations. (10 pts)

Bull’sBridge 1.47 1.47 0.74 1.31 1.12 1.13 1.04 1.37 1.49 0.91 0.92 0.96

LakeZoar 0.83 0.73 0.71 0.50 0.30 0.47 0.65 0.62 0.41 0.56 0.75 0.53

• When conducting a hypothesis test you need to provide the hypotheses, test statistic, p- value, decision, and interpretation.

• When constructing confidence intervals you need to provide both the interval and an in- terpretation.

• Calculator functions need to be given for hypothesis testing and confidence interval problems. Examples of calculator functions are TTest and TInterval.

• All interpretations need to be in terms of the problem.

Explanation / Answer

First enter data Bull’sBridge in L1 and LakeZoar in L2.

Press STAT->TESTS->2-SampTInt

Select Inpt: Data

List1: L1

List2: L2

Freq1: 1

Freq2: 1

C-level: .95

Pooled: No

Highlight Calculate and press Enter.

The 95% confidence interval for the difference in the mean PCB levels for the two locations is:

(0.39, 0.75)

We are 95% confident that the difference in the mean PCB levels for the two locations lies between 0.39 and 0.75 ppm.

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