AP Statistics Designing Studies & Experiments

A large company wants to conduct a survey to determine the proportion of its male employees who practice yoga on a daily basis. Two of its regional offices are chosen at random and all of the male employees at each office are surveyed. This plan is an example of which type of sampling?

• Cluster

• Convenience

• Simple Random

• Stratified Random

• Systematic

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Which of the following is a key distinction between well designed experiments and observational studies?

• More subjects are available for experiments than for observational studies.

• Ethical constraints prevent large-scale observational studies.

• Experiments are less costly to conduct than observational studies.

• An experiment can show a direct cause-and-effect relationship, whereas an observational study cannot.

• Tests of significance cannot be used on data collected from an observational study.

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A local television station is interested in how citizens in a small town feel about the increased sales tax proposed by the city council. The question "Are you in favor of the proposed sales tax increase that will be used to improve the sidewalks and streets in downtown?" was shown on the screen during the evening news broadcast and viewers were instructed to text their answer to the number given on the screen. This survey method could produce biased results for all of the following reasons except

• the wording of the question is biased

• a person could answer the survey multiple times.

• it uses a stratified sample rather than a simple random sample.

• the survey excludes voters who do not watch the evening news cast.

• people who feel strongly about the issue are more likely to respond.

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The oil used in gasoline engines for cars can be mineral oil, a synthetic blend (a mixture of mineral oil and synthetic oil), or pure synthetic oil. An experiment is to be conducted to determine whether oil type effects a car's engine. In previous studies, it was determined that engine size (4-cylinder, 6-cylinder, 8-cylinder) is associated with engine life, but car type (coupe, sedan, wagon) is not associated with engine life. This experiment would best be done

• by blocking on car type

• by blocking on oil type

• by blocking on engine life

• by blocking on engine size

• without blocking

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The director of an alumni association wants to estimate the mean income of the members of the class of 1999. Each person in the class of 779 graduates was given the survey and 163 of the graduates returned the survey. How could the nonresponse by the 616 graduates who did not return the survey cause the results of the survey to be biased?

• The graduates who did not respond caused the assumption of independence to be invalid.

• The graduates who did not respond changed the survey from a census to a simple random sample of graduates.

• The graduates who did not respond reduced the sample size and smaller samples are more biased than large samples.

• The graduates who did not respond may represent a group that is homogeneous with respect to income and differs from the graduates who did respond.

• The graduates who did not respond may represent a group that is heterogeneous with respect to income and is similar to the graduates who did respond.

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A consumer group for a camping and hiking magazine would like to compare a new mosquito spray made with essential oils to a traditional spray that contains DEET. The group is interested in the amount of time the spray protects the wearer from the bloodthirsty insects. Subjects will be treated and sent into a mosquito filled meadow for a 12-hour period. Which of the following is the BEST method for assigning the treatments?

• Have the subjects choose which spray theu are willing to use for the 12-hour period.

• Assign the sprays to the subjects on the basis of their camping and hiking experience without randomization.

• Give the new spray to all subjects for a 12-hour period, then give the DEET spray to all subjects for a second 12-hour period.

• Randomly assign the subjects to two groups, giving the new spray to one group and the DEET spray to the second group.

• Each subject uses a randomization device to select which spray to apply to the right side of their body. The other spray is then applied to the left side of their body.

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An education researcher would like to give a survey to a stratified random sample of students in a large school district using grade level as the strata. Which of the following would NOT be a characteristic of this stratified random sample?

• A random sample of students will be chosen.

• Each student in the population belongs to only one stratum.

• The population of students will be divided into homogeneous groups by grade level.

• Proportional numbers of students could be selected from each grade level.

• Every possible subset of the population of students in the district has the same chance of being selected.

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Students taking an exam at Westwood High School were randomly selected to receive either a peppermint candy or a similar looking candy without peppermint to determine if peppermint really improves thinking. Both groups showed an increase in test scores. This is an example of

• a successful experiment due to the peppermint treatment.

• poor design due to the lack of a control group.

• measurement bias since we do not know the difficulty level of the exam.

• the placebo effect due to the increase of scores in the non-peppermint group.

• blocking by peppermint and no peppermint candy.

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A chemical company designs an experiment to determine whether or not a new pesticide will work better than a commonly used treatment to eliminate ants. The company uses a sample of fire ants to test the new pesticide. The proportion of surviving ants that were randomly selected to receive the new pesticide was significantly lower than the proportion of ants that received the commonly used pesticide. The company concluded that the new pesticide is indeed better at killing ants. Is this a correct conclusion?

• No, because there was not a group that received no pesticide.

• No, because the experiment was only done with fire ants so the results cannot be generalized to all ants.

• Yes, because the ants were randomly selected for the two treatment groups.

• Yes, because the difference was statistically significant.

• Yes, because there was a control group to reduce the effects of confounding variables.

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