A plant physiologist conducted an experiment to determine whether mechanical stress can retard the growth of soybean plants. Young plants were randomly allocated to two groups of 13 plants each. Plants in one group were mechanically agitated by shaking for 20 minutes twice daily, while plants in the other group were not agitated. After 16 days of growth, the total stem length (cm) of each plant was measured, with the results given in the accompanying table.
Consider a t test to compare the treatments with the alternative hypothesis that stress tends to retard growth.

(a) What is the value of the t test statistic for comparing the means?
(b) The P-value for the t test is 0.0006. If α = 0.01, what is your conclusion regarding H0?

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Control Stress rl 13 13 y 30.59 27.78 2.13 1.73