Consider the following experiment. Researchers are testing i…
Consider the following experiment. Researchers are testing if fertilizer influences plant height. They collect plant height (in cm) from 17 independent plots. For 8 plots, the researchers apply fertilizer while 9 plots serve as a control and receive no fertilizer treatment. The data is shown in the table below. The “Rank” column represents the order of plant height from shortest to tallest. Plot Type Plant Height (cm) Rank Control 22.3 1 Control 22.7 2 Control 27.25 3 Control 30.03 4 Fertilizer 30.74 5 Control 30.84 6 Fertilizer 31.17 7 Fertilizer 31.33 8 Control 31.57 9 Control 32.74 10 Control 33.62 11 Control 33.79 12 Fertilizer 37.06 13 Fertilizer 39.82 14 Fertilizer 41.44 15 Fertilizer 42.72 16 Fertilizer 44.08 17 Assume that Group 1 represents Fertilizer plots and Group 2 represents Control plots. Knowing this you obtain the following information that is useful in a Mann-Whitney U test: n1 = 8, n2 = 9. 1) Calculate the Rank Sum of each group using R1 and R2 for groups 1 and 2 respectively. 2) Determine the test statistics, U1 and U2. 3) Which of the two values (U1 and U2) should you use to compare to the critical value in a Mann-Whitney U statistical table? 4) Compare your test statistic to the critical value in the U test statistic table! Be sure to state the biological interpretation of your result. The following equations may be helpful.
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