Exam 12: Experiments and Observational Surveys

A researcher wants to examine the effect of fertilizer and the effect of sunlight on the yield of tomatoes.She bought 60 tomato plants at a local garden store.She randomly assigned 30 tomato plants to be planted on the sunny side of the hill and 30 to be planted on the shady side.The 30 plants which are planted on the shady side are randomly assigned to one of three groups.The first group are grown with no fertilizer,the second group with a small amount of fertilizer,and the third group with a large amount of fertilizer.The 30 plants which are planted on the sunny side are likewise randomly assigned to one of three groups.The first group are grown with no fertilizer,the second group with a small amount of fertilizer and the third group with a large amount of fertilizer.All tomato plants are planted at the same time and are all treated alike (in terms of how much they are watered,weeded etc).Each plant is grown to maturity.The total weight of tomatoes obtained from each plant is recorded.Identify the treatments.

A researcher has developed a set of breathing exercises and would like to investigate whether they can help to reduce anxiety.She designs an experiment as follows.She will obtain a group of volunteers suffering from anxiety.They will be given a test to measure the level of their anxiety.Volunteers will be randomly assigned to one of three groups.Those in group 1 will do breathing exercises for 15 minutes per day,those in group 2 will do breathing exercises for 30 minutes per day,and those in group 3 (control group)will do no breathing exercises.After a suitable time period,each person will again take the anxiety test.The researcher will compare the average change in score for the three groups.Is it possible to double blind this experiment? Explain.

In a clinical trial,780 participants suffering from high blood pressure were randomly assigned to one of three groups.Over a one-month period,the first group received a low dosage of an experimental drug,the second group received a high dosage of the drug,and the third group received a placebo.The diastolic blood pressure of each participant was measured at the beginning and at the end of the period and the change in blood pressure was recorded.The biggest decrease in blood pressure was for those who received the low dosage of the drug.Identify the response variable measured.

A researcher wants to examine the effect of fertilizer and the effect of sunlight on the yield of tomatoes.She bought 60 tomato plants at a local garden store.She randomly assigned 30 tomato plants to be planted on the sunny side of the hill and 30 to be planted on the shady side.The 30 plants which are planted on the shady side are randomly assigned to one of three groups.The first group are grown with no fertilizer,the second group with a small amount of fertilizer,and the third group with a large amount of fertilizer.The 30 plants which are planted on the sunny side are likewise randomly assigned to one of three groups.The first group are grown with no fertilizer,the second group with a small amount of fertilizer and the third group with a large amount of fertilizer.All tomato plants are planted at the same time and are all treated alike (in terms of how much they are watered,weeded etc).Each plant is grown to maturity.The total weight of tomatoes obtained from each plant is recorded.Identify the factor(s)and the number of levels for each.

At a hospital in 1998,674 women were diagnosed with breast cancer.Five years later,88% of the Caucasian women and 83% of the African American women were still alive.Determine the nature and scope of the conclusion the study can reach.

The Asian longhorned beetle kills trees by burrowing within the trunk and branches and disrupting the sap flow.This beetle favors hardwood trees,such as maple,elm,and ash.A new pesticide will be be tested in a major metropolitan city.A statistician designs an experiment for 200 mature maple trees and randomly assigns half of the trees to receive this new pesticide,and the rest of the trees receive a control treatment. Is there any obvious way to improve this experiment to evaluate the effectiveness of this new pesticide?

A researcher wants to investigate the effectiveness of a cholesterol-lowering medication.The 450 participants are first divided into two groups - those suffering from diabetes and those not suffering from diabetes.Within each group the participants are randomly assigned to one of three groups.The first group will receive a low dose of the medication,the second group will receive a high dose of the medication,and the third group will receive a placebo.At the end of a six-month period,each person's cholesterol will be tested and the change in their cholesterol level will be recorded.The experiment is double blind.Within the group suffering from diabetes,those taking a high dose of the medication showed a marked decrease in their cholesterol level.Determine the nature and scope of the conclusion the experiment can reach.