Question

More rain for California? The changing climate will probably bring more rain to California, but we don’t know whether the additional rain will come during the

winter wet season or extend into the long dry season in spring and summer. Kenwyn Suttle of the University of California at Berkeley and his coworkers carried

out an experiment to study the effects of more rain in either season. They randomly assigned plots of open grassland to three treatments: added water equal to $20\%$of annual rainfall either during January to March (winter) or during April to June (spring), and no added water (control). Thirty-six circular plots of area $70$square meters were available (see the photo), of which $18$were used for this study. One response variable was total plant biomass, in grams per square meter, produced in a plot over a year.

(a) Outline the design of the experiment. What is this type of design called?

(b) Explain how you would randomly assign the experimental units to the three treatments. Then carry out your random assignment.

Short answer

(a) This is totally randomized system.

(b) Allot corresponding numbers to plot, mix them we, Take out six, allocate group $1$. Repeat the process till all are done.

Step-by-step solution

Given Information

To study the effect of more rains, plots re randomly assigned to three treatments.

They randomly assigned plots of open grassland to three treatments: added water equal to $20\%$of annual rainfall either during January to March (winter) or during April to June (spring), and no added water (control).

Eighteen among thirty six plots are used for study.

To identify type of design

The treatment are distributed by chance to all units in strict randomized system. The system is strictly randomized system.

The description is:

To explain random assignment of groups to three treatments.

• For $18$plots, assign numbers from $1-18$in paper slips.
• Mix it in utensil and take out six pieces. Allocate them group$1$
• Draw six again and allocate them group $2$.
• Repeat the step again and allocate group $3$.
• Compare total biomass produced in three groups after one year.