Exam 11: Experiments and Observational Studies

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?

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?

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.

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 is 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 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.

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?

Researchers reported that going to the gym regularly increases your chance of finding a high paying job.These findings were based on incomes reported by 200 active members of a gym and 200 people who do not belong to a gym.Why is this conclusion not justified?

A manufacturer of tennis rackets has designed a new racket and would like to investigate whether players will prefer 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 company's previous racket second.Each player will serve 30 times with each racket.Then the percentage of good serves with the two rackets will 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 players use.If the group of volunteers consists of 50 professional tennis players and 50 beginners,how could the experiment be improved?

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 1-10.Identify the factor(s)in the experiment and the number of levels for each.

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.

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.

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.

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?

An ice cream company wants to introduce a new flavor.They are considering two possibilities - Mint Delight and Chocolate Fiesta.They want to know which one customers will prefer.Design an experiment to investigate this question.

A manufacturer of tennis rackets has designed a new racket and would like to compare it to their previous design.Suggest an appropriate experiment.

780 patients suffering from high blood pressure were randomly assigned to one of three groups.Over a four-month period,the first group received an experimental drug,the second group received a placebo,and the third group received no treatment.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 drug.

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.

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.

A statistics instructor 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 60 volunteer statistics students. Volunteers will be randomly assigned to one of two groups.Group 1 will be taught the statistics course using method A and group 2 will be taught using method B.Other than the different methods,everything else will be similar for the two groups.For example,both groups will have the same teacher,the same lecture room,the same amount of time devoted to the course.At the end of the semester,students will all take the same test.Then the scores for the two groups will be compared.If the first group has a mean score of 67.7 with a standard deviation of 13.4 and the second group a mean score of 71.6 with a standard deviation of 11.2,do you think that this result is statistically significant? Explain.

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 osteoporosis.Identify the subjects studied.

An educational researcher used school records to determine that,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.