Briefly describe the experimental design you would choose for each of the follow

Question

Briefly describe the experimental design you would choose for each of the following situations, and explain why.

(a) A plant breeder wishes to study the effects of soil drainage and variety of tulip bulbs on flower production. Twelve 3 m by 10 m experimental sites are available in a garden. Each site is a .5 m–deep trench. Soil drainage is changed by adding varying amounts of sand to a clay soil (more sand improves drainage), mixing the two well, and placing the mixture in the trench. The bulbs are then planted in the soils, and flower production is measured the following spring. It is felt that four different levels of soil drainage would suffice, and there are fifteen tulip varieties that need to be studied.

(b) It’s Girl Scout cookie time, and the Girl Scout leaders want to find out how to sell even more cookies (make more dough?) in the future. The

variables they have to work with are type of sales (two levels: door-to- door sales or table sales at grocery stores, malls, etc.) and cookie selec- tion (four levels comprising four different “menus” of cookies offered to customers). Administratively, the Girl Scouts are organized into “councils” consisting of many “troops” of 30-or-so girls each. Each Troop in the experiment will be assigned a menu and a sales type for the year, and for logistical reasons, all the troops in a given council should have the same cookie selection. Sixteen councils have agreed to participate in the experiment.

(c) Rodent activity may be affected by photoperiod patterns. We wish to test this possibility by treating newly-weaned mouse pups with three different treatments. Treatment 1 is a control with the mice getting 14 hours of light and 10 hours of dark per day. Treatment 2 also has 14 hours of light, but the 10 hours of dark are replaced by 10 hours of a low light level. Treatment 3 has 24 hours of full light.

Mice will be housed in individual cages, and motion detectors con- nected to computers will record activity. We can use 24 cages, but the computer equipment must be shared and is only available to us for 1 month.

Mice should be on a treatment for 3 days—one day to adjust and then 2 days to take measurements. We may use each mouse for more than one treatment, but if we do, there should be 7 days of standard photoperiod between treatments. We expect large subject-to-subject variation. There may or may not be a change in activity as the rat pups age; we don’t know.

Explanation / Answer

a) In this case we would go with a Randomized complete block design because twelve 3 m by 10 m experimental sites are available in a garden to accoun tfor any variation in the whole field. And treatments are applied at random to the bulbs planted.

b) In this case we would go for a 2 * 4 factorial design experiment, since, both the independent variables - type of sales and cookie selection have different levels.

c) In this case we would go with a Latin square design because, we have three treatment combinations and different types of light conditions for each mice.

c)

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