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Chapter 6: Planning and Conducting an Experiment or Study

Created by: CK-12

Chapter Outline

Chapter Summary

Part One: Multiple Choice

  1. A researcher performs an experiment to see if mice can learn their way through a maze better when given a high-protein diet and vitamin supplements. She carefully designs and implements a study with the random assignment of the mice into treatment groups and observes that the mice on the special diet and supplements have significantly lower maze times than those on normal diets. She obtains a second group of mice and performs the experiment again. This is most appropriately called:
    1. Matched pairs design
    2. Repeated measures
    3. Replication
    4. Randomized block design
    5. Double blind experiment
  2. Which of the following terms does not apply to experimental design?
    1. Randomization
    2. Stratification
    3. Blocking
    4. Cause and effect relationships
    5. Placebo
  3. An exit pollster is given training on how to spot the different types of voters who would typically represent a good cross-section of opinions and political preferences for the population of all voters. This type of sampling is called:
    1. Cluster sampling
    2. Stratified sampling
    3. Judgment sampling
    4. Systematic sampling
    5. Quota sampling

Use the following scenario to answer questions 4 and 5. A school performs the following procedure to gain information about the effectiveness of an agenda book in improving student performance. In September, 100 students are selected at random from the school’s roster. The interviewer then asks the selected students if they intend to use their agenda books regularly to keep track of their assignments. Once the interviewer has 10 students who will use their book and 10 students who will not, the rest of the students are dismissed. Next, the selected students’ current averages are recorded. At the end of the year, the grades for each group are compared, and overall, the agenda-book group has higher grades than the non-agenda group. The school concludes that using an agenda book increases student performance.

  1. Which of the following is true about this situation?
    1. The response variable is using an agenda book.
    2. The explanatory variable is grades.
    3. This is an experiment, because the participants were chosen randomly.
    4. The school should have stratified by gender.
    5. This is an observational study, because no treatment is imposed.
  2. Which of the following is not true about this situation?
    1. The school cannot conclude a cause-and-effect relationship, because there is most likely a lurking variable that is responsible for the differences in grades.
    2. This is not an example of a matched pairs design.
    3. The school can safely conclude that the grade improvement is due to the use of an agenda book.
    4. Blocking on previous grade performance would help isolate the effects of potential confounding variables.
    5. Incorrect response bias could affect the selection of the sample.

Part Two: Open-Ended Questions

  1. During the 2004 presidential election, early exit polling indicated that Democratic candidate John Kerry was doing better than expected in some eastern states against incumbent George W. Bush, causing some to even predict that he might win the overall election. These results proved to be incorrect. Again, in the 2008 New Hampshire Democratic primary, pre-election polling showed Senator Barack Obama winning the primary. It was, in fact, Senator Hillary Clinton who comfortably won the contest. These problems with exit polling lead to many reactions, ranging from misunderstanding the science of polling, to mistrust of all statistical data, to vast conspiracy theories. The Daily Show from Comedy Central did a parody of problems with polling. Watch the clip online at the following link. Please note that while “bleeped out,” there is language in this clip that some may consider inappropriate or offensive. http://www.thedailyshow.com/video/index.jhtml?videoId=156231&title=team-daily-polls What type of bias is the primary focus of this non-scientific, yet humorous, look at polling?
  2. Environmental Sex Determination is a scientific phenomenon observed in many reptiles in which air temperature when eggs are growing tends to affect the proportion of eggs that develop into male or female animals. This has implications for attempts to breed endangered species, as an increased number of females can lead to higher birth rates when attempting to repopulate certain areas. Researchers in the Galapagos wanted to see if the Galapagos Giant Tortoise eggs were also prone to this effect. The original study incubated eggs at three different temperatures: 25.50^\circ C, 29.50^\circ C, and 33.50^\circ C. Let’s say you had 9 female tortoises, and there was no reason to believe that there was a significant difference in eggs from these tortoises.
    1. Explain how you would use a randomized design to assign the treatments and carry out the experiment.
    2. If the nine tortoises were composed of three tortoises each of three different species, how would you design the experiment differently if you thought that there might be variations in response to the treatments?
  3. A researcher who wants to test a new acne medication obtains a group of volunteers who are teenagers taking the same acne medication to participate in a study comparing the new medication with the standard prescription. There are 12 participants in the study. Data on their gender, age, and the severity of their condition are given in the following table:
Subject Number Gender Age Severity
1 M 14 Mild
2 M 18 Severe
3 M 16 Moderate
4 F 16 Severe
5 F 13 Severe
6 M 17 Moderate
7 F 15 Mild
8 M 14 Severe
9 F 13 Moderate
10 F 17 Moderate
11 F 18 Mild
12 M 15 Mild

(a) Identify the treatments, and explain how the researcher could use blinding to improve the study.

(b) Explain how you would use a completely randomized design to assign the subjects to treatment groups.

(c) The researcher believes that gender and age are not significant factors, but is concerned that the original severity of the condition may have an effect on the response to the new medication. Explain how you would assign treatment groups while blocking for severity.

(d) If the researcher chose to ignore pre-existing condition and decided that both gender and age could be important factors, he or she might use a matched pairs design. Identify which subjects you would place in each of the 6 matched pairs, and provide a justification of how you made your choice.

(e) Why would you avoid a repeated measures design for this study?

Keywords

Bias

Blind experiment

Blocking

Census

Cluster sampling

Confounding variables

Control group

Convenience sampling

Double blind experiment

Experiment

Incorrect response bias

Incorrect sampling frame

Judgement sampling

Lurking variable

Margin of error

Matched pairs design

Multi-stage sampling

Non-response bias

Observational study

Placebo

Placebo effect

Questionnaire bias

Quota sampling

Random sample

Randomization

Randomized block design

Randomly assigned

Repeated measures design

Replication

Response bias

Sample

Sampling error

Sampling frame

Seed value

Simple random sample

Size bias

Stratified sampling

Systematic sampling

Treatment

Undercoverage

Voluntary response bias

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Date Created:

Aug 20, 2013

Last Modified:

Aug 21, 2014
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