Question

Researchers interested in lead exposure due to car exhaust sampled the blood of 52 police officers subjected to constant inhalation of automobile exhaust fumes while working traffic enforcement in a primarily urban environment. The blood samples of these officers had an average lead concentration of 122.31 µg/l and a SD of 38.75 µg/l; a previous study of individuals from a nearby suburb, with no history of exposure, found an average blood level concentration of 35 µg/l.
Required:
a. Write down the hypotheses that would be appropriate for testing if the police officers appear to have been exposed to a higher concentration of lead.
b. Explicitly state and check all conditions necessary for inference on these data.
c. Test the hypothesis that the downtown police officers have a higher lead exposure than the group in the previous study. Interpret your results in context.
d. Based on your preceding result, without performing a calculation, would a 99% confidence interval for the average blood concentration level of police officers contain 35 ug/l?

Answer 1

Step-by-step explanation:

n = 52

x bar = 122.31

standard deviation sd = 38.75

1. the hypothesis:

null hypothesis

h0: μ ≤ 35

alternative hypothesis

h1: μ > 35

2.

we have been given the sd of the sample but not that of the population. so what we are supposed to use here is the t test and not the z test. the following conditions have to be met.

• population has to be normal
• sample size has to be more than 30. we have sample size = 52 in this question.

3.

= $\frac{122.31-35}{38.75/\sqrt{52} }$

= 87.31/5.37

= 16.26

using the T distribution function in excel, the p value was calculated and found to be approximately equal to 0.

TDIST(16.26, 51, 1)

since p value is very small we reject the null and accept the alternate hypothesis.

4. from the result above the answer to this question is yes