A major undertaking in previous years involved retrofitting fertilizer productio

Question

A major undertaking in previous years involved retrofitting fertilizer production lines with LEV systems to reduce ammonia exposures among line workers. Four of your 10 fertilizer plants have been modified, with another 6 scheduled for the upcoming year. Your industrial hygiene team has been collecting ammonia exposure data in all of your facilities for compliance purposes. You decide to analyze the data to determine if the new LEV systems are significantly reducing ammonia exposures, as intended. The lead IH in charge of sampling emailed you the exposure records for all fertilizer production facilities. Data on worker exposures from two similar facilities (one with and one without the LEV system) are provided below: acility Line1 Line2 Line3 Line4 Line oc1 2 Maint 1 Maint2 Floor down)/task right) sup tsburgh 35 ppm 25 ppm 15 ppm 10 ppm 7 ppm 5 ppm 1 ppm no LEV) pm PpmPpm Omaha 5ppm 20 ppm 14 ppm Pump 0 ppm 5 ppm 2 ppm 3 LEV) ailed opm ppm ppm

Explanation / Answer

Correct answer Option (A) Mann - Whitney test

The Mann-Whitney U test is used to compare differences between two independent groups when the dependent variable is either ordinal or continuous, but not normally distributed. For example, you could use the Mann-Whitney U test to understand whether attitudes towards pay discrimination, where attitudes are measured on an ordinal scale, differ based on gender (i.e., your dependent variable would be "attitudes towards pay discrimination" and your independent variable would be "gender", which has two groups: "male" and "female"). Alternately, you could use the Mann-Whitney U test to understand whether salaries, measured on a continuous scale, differed based on educational level (i.e., your dependent variable would be "salary" and your independent variable would be "educational level", which has two groups: "high school" and "university"). The Mann-Whitney U test is often considered the nonparametric alternative to the independent t-test although this is not always the case.

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