Chapter 5.3, Problem 2Q

The production of a nationally marketed detergent results in certain workers receiving prolonged exposures to a Bacillus subtilis enzyme. Nineteen workers were tested to determine the effects of those exposures, if any, on various respiratory functions. One such function, air-flow rate, is measured by computing the ratio of a person’s forced expiratory volume $\left({\text{FEV}}_{\text{1}}\right)$ to his or her vital capacity $\left(\text{VC}\right)$. (Vital capacity is the maximum volume of air a person can exhale after taking as deep a breath as possible; ${\text{FEV}}_{\text{1}}$ is the maximum volume of air a person can exhale in one second.) In persons with no lung dysfunction, the “norm” for ${\text{FEV}}_{\text{1}}\text{/VC}$ ratios is 0.80. Based on the following data $\left(\text{175}\right)$, is it believable that exposure to the Bacillus subtilis enzyme has no effect on the ${\text{FEV}}_{\text{1}}\text{/VC}$ ratio? Answer the question by constructing a 95% confidence interval. Assume that ${\text{FEV}}_{\text{1}}\text{/VC}$ ratios are normally distributed with $\sigma =0.09$.

Subject	${\text{FEV}}_1\text{/VC}$	Subject	${\text{FEV}}_1\text{/VC}$
RH	0.61	WS	0.78
RB	0.70	RV	0.84
MB	0.63	EN	0.83
DM	0.76	WD	0.82
WB	0.67	FR	0.74
RB	0.72	PD	0.85
BF	0.64	EB	0.73
JT	0.82	PC	0.85
PS	0.88	RW	0.87
RB	0.82