Exam 11: Experiments and Observational Studies

A researcher would like to investigate whether people suffering from insomnia can be helped by taking regular yoga classes or by reducing their intake of caffeine.Design an appropriate experiment.Be sure to identify the factors,levels,treatments,and response variable.

An educational researcher has designed two different methods for teaching a statistics course and would like to investigate which is more effective.He designs an experiment as follows.He will obtain a group of volunteer statistics students. Volunteers will be randomly assigned to one of two groups.Group 1 will be taught the statistics course by Anna Clark using method A and group 2 will be taught by Bob Beauman using method B.At the end of the semester,students will all take the same test.Then the scores for the two groups will be compared.Identify the flaw(s)in this experiment and suggest a way of improving the experiment.

Explain the difference between an observational study and an experiment.

780 participants suffering from depression were randomly assigned to one of three groups.Over a four-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.At the end of the period each participant rated their mood on a scale of 1-5.Identify the treatments.

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.

Researchers reported that for men,being unmarried increases the risk of depression.These findings were based on the medical records of 400 married men and 500 unmarried men.Why is this conclusion not justified?

A manufacturer of tennis rackets would like to test their new racket.The company sponsors 10 tennis players who will be playing at Wimbledon.To test the racket,they have each player serve 30 times with their old racket.Then they have each player serve 30 times with the new racket.They compare the percentage of good serves with the two rackets.Identify the flaw(s)in this experiment and suggest some improvements.

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.

780 men suffering from high blood pressure were randomly assigned to one of two groups.Over a four-month period,the first group received an experimental drug and the second group received a placebo.A larger decrease in diastolic blood pressure was observed for those who received the drug.The experiment was double-blind.Determine the nature and scope of the conclusion the study can reach.

Researchers reported that unmarried men are more likely to suffer from clinical depression than married men.These findings were based on the marriage histories of 700 men suffering from depression and 600 men not suffering from depression.Determine the nature and scope of the conclusion the study can reach.

Among a group of Canadian men who were tracked for ten years,those who had scored over 130 on intelligence tests were more likely to suffer severe depression than those who had scored below 130 on intelligence tests.Identify the parameter of interest.

A researcher would like to investigate whether people suffering from insomnia can be helped by taking yoga classes.She designs an experiment as follows.She will obtain a group of volunteers who are suffering from insomnia and who do not currently practice yoga.Each person's degree of insomnia at the start of the experiment will be evaluated.She will investigate whether yoga classes every day or three times per week are more effective.So the factor yoga will have 3 levels (no yoga,yoga three times a week,yoga every day).Each volunteer will choose which group they would like to be part of.At the end of a suitable time period,for example two months,each person's degree of insomnia will again be evaluated.The improvement for the three groups will then be compared.The person evaluating the insomnia levels will be blinded to which group the patients were in.Identify the most serious flaw in this experiment.

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 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 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.

An examination of the medical records of 10,000 women showed that those who were short and fair skinned had a higher risk of osteoporosis.

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.A researcher concludes that being Caucasian causes women with breast cancer an increased chance of surviving five years.Since there is no random assignment and there may have been lurking variables,this conclusion is not justified.Which of the following are possible lurking variables? I: Income II: Neighborhood where patient lives III: Quality of health care IV: Diet V: Number of years surviving since diagnosis

A researcher has developed a set of breathing exercises and would like to investigate whether they can help to reduce anxiety.She wonders whether the breathing exercises for 15 minutes or for 30 minutes would be more effective.Design an appropriate experiment.

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 pharmaceutical company has developed a medication which they believe will help to reduce the pain of arthritis.They would like to test the medication at two different dosage levels.They design an experiment as follows to test the medication.They will obtain a group of volunteers who suffer from arthritis.A doctor from the pharmaceutical company will evaluate each patient's condition at the start of the experiment.Volunteers will be randomly assigned to one of three groups.Each day for the duration of the experiment,patients in group 1 will receive a low dose of the medication,patients in group 2 will receive a higher dose of the medication,and patients in group 3 will receive a placebo.After a suitable amount of time (two months,for example),the same doctor will evaluate each patient's progress.Based on the amount of inflammation and the patient's report on the amount of pain,the doctor will give each patient a numerical score to represent their improvement.The amount of improvement for the three groups will then be compared.The researchers will have the technicians administering the medication blinded to whether patients receive a low dose,a high dose,or a placebo.Identify the most serious flaw in this experiment.

An agricultural researcher wishes to compare the yield of four different varieties of wheat.64 plots of land are available for an experiment.On each plot of land one of the varieties of wheat will be grown.At the end of the experiment the yield for the different varieties will be compared.32 of the plots are at one site (site A)and the other 32 are at another site (site B).The soil at site A differs significantly from the soil at site B.If the researcher wishes to design an experiment using randomized block design,how could the wheat varieties be assigned to the different plots?