Cortisol is a hormone that plays an important role in mediating stress. There is growing awareness that exposure of outdoor workers to pollutants may impact cortisol levels. The article "Plasma Cortisol Concentration and Lifestyle in a Population of Outdoor Workers" (Intl. J. of Envir. Health Res., 2011: 62-71) reported on a study involving three groups of police officers:
(1) Traffic police (TP),
(2) Drivers (D), and
(3) Other duties (O). Here is summary data on cortisol concentration (ng/ml) for a subset of the officers who neither drank nor smoked.

Assuming that the standard assumptions for one-way ANOVA are satisfied, carry out a test at significance level .05 to decide whether true average cortisol concentration is different for the three groups. The investigators used more sophisticated statistical methodology (multiple regression) to assess the impact of age, length of employment, and drinking and smoking status on cortisol concentration; taking these factors into account, concentration appeared to be significantly higher in the TP group than in the other two groups.

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Group Sample Size Mean SD TP 47 36 50 174.7 50.9 160.2 37.2 153.5 45.9