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 (FEV₁) to his or her vital capacity (VC). (Vital capacity is the maximum volume of air a person can exhale after taking as deep a breath as possible; FEV₁ is the maximum volume of air a person can exhale in one second.) In persons with no lung dysfunction, the "norm" for FEV1/VC ratios is 0.80. Based on the following data (164), is it believable that exposure to the Bacillus subtilis enzyme has no effect on the FEV₁/VC ratio? Answer the question by constructing a 95% confidence interval. Assume that FEV₁/VC ratios are normally distributed with σ = 0.09.

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Subject FEVI/VC Subject FEV/VC RH 0.61 RB MB 0.63 DM 0.76 WB 0.67 RB 0.72 BF JT PS RB 082 WS RV EN WD FR PD EB PC RW 0.78 0.84 0.83 0.82 0.74 0.85 0.73 0.85 0.87 0.70 0.64 0.82 0.88