Exam 12: Experiments and Observational Surveys

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?

In a clinical trial,each participant will receive a placebo,a low dosage of a drug,or a high dosage of the drug.The participants consist of 90 men and 90 women.The 90 men are randomly divided into three groups of 30.Each group of men is randomly assigned to a different treatment (placebo,low dose,or high dose).Likewise,the 90 women are randomly divided into three groups of 30.Each group of women is randomly assigned to a different treatment (placebo,low dose,or high dose).Is this a completely randomized design or a randomized block design? Explain your answer.

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.

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 completely randomized design,how could the wheat varieties be assigned to the different plots?

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.Identify the factor(s)and any blocking variables and the number of levels for each.

An education researcher was interested in examining the effect of the teaching method and the effect of the particular teacher on students' scores on a reading test.In a study,there are four different teachers (Juliana,Felix,Sonia,and Helen)and three different teaching methods (A,B,and C).The number of students participating in the study is 258.Students are randomly assigned to a teaching method and teacher.Those who studied with Sonia using method B achieved the highest scores.Identify the response variable measured.

A researcher would like to compare the effectiveness of two competing study courses both of which claim to raise students' SAT scores.He would also like investigate whether students can benefit from listening to a certain type of music while they study.Design an appropriate experiment.Be sure to identify the factors,levels,treatments,and response variable.

A manufacturer of tennis rackets has designed a new racket and would like to compare it to their previous design.The company obtains 100 volunteer tennis players.Volunteers are randomly assigned to one of two groups.Group 1 will use the company's previous racket first and the new racket second.Group 2 will use the new racket first and the previous racket second.Each player will serve 30 times with each racket.The percentage of good serves with the two rackets will then be compared.The players are blinded to which racket they are using.Also,the person recording the percentage of good serves is blinded to which racket the player is using.If the group of volunteers consists of 60 professional tennis players and 40 beginners,how could the experiment be improved?

A new type of pain reliever is administered to 30 consenting post-operative patients in various hospitals.Although the pain reliever has already been tested for safety and effectiveness,this experiment is to observe and categorize any side-effects.Because of maturity and body mass,it is decided to test the adults separately from the children. The grouping of the adults separate from the children is an example of what?

780 men suffering from high blood pressure 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.The biggest decrease in blood pressure was for those who received the low dosage of the drug.Identify the subjects studied.

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.Why is this conclusion not justified?

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 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 would then be compared.They will also ensure that the technicians administering the supplements are blinded to whether patients receive a low dose,a high dose,or a placebo.Identify the flaw(s)in this experiment.

An educational researcher used school records to determine that in the year 2000 in one school district,84% of children living in two-parent homes graduated high school while 75% of children living in single-parent homes graduated high school.Determine the parameter of interest.

A medical researcher believes that supplements of glucosamine can help to reduce the pain of arthritis.She would like to test the supplement at two different dosage levels.She designs an experiment as follows to test her conjecture.She will obtain a group of 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 two groups.Each day for the duration of the experiment,patients in group 1 will receive a low dose of glucosamine,patients in group 2 will receive a higher dose of glucosamine.After a suitable amount of time (two months,for example),the 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 two groups would then be compared.She will have the evaluating doctor and the technicians administering the supplements blinded to whether patients receive a low dose or high dose.Identify the most serious flaw in this experiment.

A researcher wants to investigate whether different forms of exercise can be used to help hyperactive children.A group of 90 children is divided into two groups according to age - those aged 9-12 and those aged 5-9.Within each age group the children are randomly assigned to one of three groups.The first group will just do their normal exercise.The second group will be given an additional exercise routine (moderate).The third group will be given an additional exercise routine (strenuous).At the end of a four month period parents will be asked to evaluate their children's progress.Identify the treatments.

An education researcher was interested in examining the effect of the teaching method and the teacher on students' reading levels.257 students participated in an experiment.There were two different teachers (Juliana and Felix)and three different teaching methods (A,B,and C).Students were randomly assigned to a teaching method and teacher.At the end of the semester the students took a reading test on which they received a score out of 20.Students who studied with Felix using method B achieved the highest scores.

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 volunteer insomniacs who do not currently practice yoga.Each person's degree of insomnia at the start of the experiment will be evaluated.Volunteers will be randomly assigned to one of three groups.Those in group 1 will practice yoga every day,those in group 2 will practice 3 times per week,and those in group 3 will not practice yoga.At the end of a suitable time period each person's degree of insomnia will again be evaluated.The improvement for the three groups will then be compared.Explain why it is important to assign volunteers to groups at random rather than letting them choose their own group.

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 parameter of interest.