1.Some researchers have speculated that plants emerging white or bleached and eventually dying might be controlled with weed and soil treatments. An experiment was conducted to compare plant growth with soil and weeds treated with one of two herbicides. In a section of a field containing 150 affected plants, 50 were selected randomly throughout the field and assigned to receive herbicide A. The remainder received herbicide B. Soil and weeds for each plant were treated with the appropriate herbicide, and at the end of the study period the amount of new growth (in centimeters) was recorded for each plant. The results obtained are shown.

Herbicide A: X₁= 12.4 centimeters, s₁= 4 centimeters

Herbicide B: X₂= 18.7 centimeters, s₂= 3 centimeters

Suppose we wished to determine whether there is a difference in height for the seedlings treated with the different herbicides. To answer this question, we decide to test the hypotheses H₀: _{2 1}= 0 and H_a: _{2 1} 0. Find the 90% confidence interval for _{2 1}and make a conclusion based on that confidence interval.

a

The 90% confidence interval is 6.3 7.37. The p-value is less than 0.10.

b

The 90% confidence interval is 6.3 1.05. I would not reject the null hypothesis of no difference at the 0.10 level.

c

The 90% confidence interval is 6.3 5.23. I would not reject the null hypothesis of no difference at the 0.10 level.

d

The 90% confidence interval is 6.3 5.23. I would reject the null hypothesis of no difference at the 0.10 level.

e

The 90% confidence interval is 6.3 1.05. I would reject the null hypothesis of no difference at the 0.10 level.

2.Which of the following is an example of a matched-pairs design?

a

Group individuals randomly and compare their results with two different treatments.

b

Compare treatment results of one group with the state average results to the treatment.

c

Group individuals into pairs based on age and gender, and then assign treatments randomly within each pair.

d

A doctor calculates the average positive results to a treatment and determines whether this average is greater than 50%.

e

None of the choices qualify as an example of a matched-pairs design.