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Explain the difference between an observational study and an experiment. In your explanation, be sure to discuss the circumstances in which each is appropriate.

What is a closed question? What is an open question? Discuss the advantages and disadvantages of each type of question.

What does it mean when sampling is done without replacement?

To help assess student learning in her developmental math courses, a mathematics professor at a community college implemented pre- and posttests for her developmental math students. A knowledge-gained score was obtained by taking the difference of the two test scores. (a) What type of experimental design is this? (b) What is the response variable in this experiment? (c) What is the treatment?

True or False: Observational studies do not allow a researcher to claim causation.

True or False: When conducting a cluster sample, it is better to have fewer clusters with more individuals when the clusters are heterogeneous.

Identify the type of sampling used. To estimate the percentage of defects in a recent manufacturing batch, a quality-control manager at Intel selects every 8 th chip that comes off the assembly line starting with the 3rd until she obtains a sample of 140 chips.

Identify the type of sampling used. To determine customer opinion of their boarding policy, Southwest Airlines randomly selects 60 flights during certain week and surveys all passengers on the flights.

Researchers wanted to evaluate whether ginkgo, an over-the-counter herb marketed as enhancing memory, improves memory in elderly adults as measured by objective tests. To do this, they recruited 98 men and 132 women older than 60 years and in good health. Participants were randomly assigned to receive ginkgo, \(40 \mathrm{mg} 3\) times per day, or a matching placebo. The measure of memory improvement was determined by a standardized test of learning and memory. After 6 weeks of treatment, the data indicated that ginkgo did not increase performance on standard tests of learning, memory, attention, and concentration. These data suggest that, when taken following the manufacturer's instructions, ginkgo provides no measurable increase in memory or related cognitive function to adults with healthy cognitive function. (Source: "Ginkgo for Memory Enhancement," Paul R. Solomon, et. al.; Journal of the American Medical Association 288(2002): 835-840)$ (a) What type of experimental design is this? (b) What is the population being studied? (c) What is the response variable in this study? (d) What is the factor? What are the treatments? (e) Identify the experimental units. (f) Draw a diagram similar to Figure 6 or 7 to illustrate the design.

Determine whether the study depicts an observational study or an experiment. Seventh-grade students are randomly divided into two groups. One group is taught math using traditional techniques; the other is taught math using a reform method. After 1 year, each group is given an achievement test to compare its proficiency with that of the other group.