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 why.

(a) We wish to determine the amount of salt to put in a microwave popcorn so that it has the best overall acceptability. We will test three levels of salt: low, medium, and high. We have recruited 25 volunteers to taste popcorn, and while we expect the individuals to be reasonably consistent in their own personal ratings, we expect large volunteer to volunteer differences in overall ratings.

(b) Some brands of golf balls claim to fly farther. To test this claim, you devise a mechanical golf ball whacker which will strike the golf balls with the same power and stroke time after time. Ten balls of each of six brands will be struck once by the device and measured for distance traveled. Wind speed, which will affect the distance traveled, is vari- able and unpredictable, but can be measured.

(c) We wish to study the effects of two food additives (plus a control treatment for a total of three treatments) on the milk productivity of cows. We have three large herds available, each of a different breed, and we expect breed to breed differences in the response. Furthermore, we ex- pect an age effect, which we make explicit by dividing cows into three groups: those which have had 0, 1, and 2 or more previous calves. We have enough resources to study 27 animals through one breeding cycle.

Explanation / Answer

a) Randomized block design. Treatment factor is the salt levels and block factor is the 25 volunteers. We must block volunteers as we expect large volunteer to volunter differences. In addition, we don't expect salt levels interact with volunteers.

b) Repeated measure design because each player should measure each ball.

c) Full factorial design since three factors all have 3 levels and 27 animals are enough to run a full factorial design (3 X 3 X 3 = 27)

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