Exam 12: Experiments and Observational Surveys

400 patients suffering from chronic back pain were randomly assigned to one of two groups.Over a four-month period,the first group received acupuncture treatments and the second group received a placebo.Patients who received acupuncture treatments improved more than those who received the placebo.

An examination of the medical records of 10,000 women who died between 1990 and 2000 showed that those who had taken steroids had a higher risk of osteoperosis.Identify the subjects studied.

An employer suspects that on Mondays the percentage of employees absent from work is higher than on other days.Design a way he could find out whether there is any merit to his belief.Should he use an experiment or an observational study? He would like to have the information as soon as possible.

A medical researcher designs an experiment to test whether supplements of glucosamine can help to reduce the pain of arthritis.She will obtain a group of 90 volunteers who suffer from arthritis.Each patient's condition will be evaluated by a doctor at the start of the experiment.Volunteers will be randomly assigned to one of three groups.Each day patients in group 1 will receive a low dose of glucosamine,patients in group 2 will receive a higher dose of glucosamine,and patients in group 3 will receive a placebo.After a suitable amount of time,the doctor will evaluate each patient's progress.Based on the amount of inflammation and pain,the doctor will give each patient a numerical score to represent their improvement.The researcher will then compare the improvement for the three groups.Describe a strategy to randomly assign the 90 volunteers to the three treatments.

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 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.Within each group of 30 plants,she randomly assigned plants to one of three groups.The first group is 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.The person evaluating the results does not know which tomatoes received fertilizer or which were grown on the sunny side.Within both groups (those grown on the sunny side and those grown on the shady side)tomatoes grown with a large amount of fertilizer yielded the most tomatoes.Determine the nature and scope of the conclusion the experiment can reach.

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.

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.

An education researcher wishes to assess the effectiveness of three different methods for teaching young children to read.The 380 children participating in the study are divided into three groups.The study runs for six months.The children in the first group are taught using method A,the children in the second group are taught using method B,and the children in the third group are taught using method C.At the end of the six months,the reading ability of the children in the different groups is assessed.Why is it important to use random assignment when dividing the children into three groups?

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.The researcher wishes to design an experiment.In this example,why might a randomized block design,with blocking by soil type,be preferable to a completely randomized design?

An exercise physiologist has designed two alternative training regimes which he hopes will enable middle distance runners to improve their times at the 800 metres.He wants to know which regime will work better.Design an experiment which will allow him to investigate this question.Assume that all the athletic coaches in a district are prepared to participate and assume that all athletes training with a particular coach will follow the same regime.Be sure to identify the factors,the levels,treatments,and response variable.

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 pharmaceutical company will be testing a new "one-dosage fits all" medication for treating depression.The pharmaceutical company has 100 willing test subjects that will undergo a 30-day,double-blind experiment.The experiment uses the following diagram as a guide for administering the medication at various doses,from 5% to 125%. What is the most obvious factor missing from this proposed experiment?

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.

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.Since there is no random assignment,this conclusion is not justified because there may be lurking variables.Which of the following are possible lurking variables? I: Rate of depression II: Income III: Type of employment IV: Age V: Gender

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?

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 patients did not know whether they were receiving the drug or the placebo.Neither the technicians administering the treatments nor the physicians evaluating the results knew which participants had received the drug and which the placebo.

Among a group of 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.

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.

A clothing manufacturer is curious if celebrity endorsements will influence a customer's decision in buying its products.This clothing manufacturer premieres its latest series of commercials privately to two separate groups of potential shoppers.One group will see a series of commercials without celebrities,and one group will see a series of commercials with celebrities.Furthermore,the manufacturer decides to split up the male shoppers from the female shoppers. Grouping the shoppers together by gender is an example of what?