1. Warm Up
Compare and contrast the following concepts as they relate to designing studies and experiments: Stratified Random Sample Blocking How are they similar and how are they different?

2. Experimental Design Practice
Everyone will get a description of 4 experiments we will design today. We will work on these one at a time.
When instructed to begin, work with your partner to design an experiment for the scenario described.
You should create a chart, diagram or table that clearly explains your experiment. Be sure to indicate if your experiment uses blocking or matched pairs and where control, randomization and replication are used.

3. Experimental Design Practice
For each scenario we will randomly choose 3 groups to present their experimental design. Show your plan on the document camera and be prepared to answer questions from the audience.
The group judged (by the class) to have the best design will receive extra credit.
Creativity should enhance your chances of winning, but only if it improves the experimental design.

4. You will be shown a multiple choice question related to the material from Chapter 4. A student will be selected at random, if they answer correctly they get one point for their team. If they answer incorrectly another student will be randomly selected. If there are 3 incorrect answers the question is skipped. Each member of each team will get the extra credit points won by their table.

5. 1) A maple sugar manufacturer wants to estimate the average trunk diameter of Sugar Maples trees in a large forest. There are too many trees to list them all and take a SRS, so he divides the forest into several hundred 10 meter by 10 meter plots, selects 25 plots at random, and measures the diameter of every Sugar Maple in each one. This is an example of a (a) multistage sample. (b) stratified sample. (c) simple random sample. (d) cluster sample. (e) convenience sample.

6. 2. A survey was done in the town of Mechanicsville to estimate the proportion of cars that are red. A random sample of 25 cars from a student parking lot at Lee-Davis High School was taken. Which of the following statements is not correct? (a) This sample may not be representative of the cars in Mechanicsville because mainly students park at Lee-Davis High School. (b) If the particular parking space is vacant, we can simply select another parking space at random because it is unlikely that a space being vacant is related to the color of the car. (c) It would an error to simply select the first 25 parking spaces in the lot closest to the auditorium because there are a number of parking spaces there reserved for Drivers Ed vehicles, whose primary color is white. (d) A different team doing the sampling independently would likely obtain a different answer for their sample proportion. (e) The results will be the same regardless of the time of day that the sample is taken.

7. 3. A nutritionist wants to study the effect of storage time (6, 12, and 18 months) on the amount of vitamin C present in freeze dried fruit when stored for these lengths of time. Vitamin C is measured in milligrams per 100 milligrams of fruit. Six fruit packs were randomly assigned to each of the three storage times. The treatment, experimental unit, and response are respectively: (a) A specific storage time, amount of vitamin C, a fruit pack (b) A fruit pack, amount of vitamin C, a specific storage time (c) Random assignment, a fruit pack, amount of vitamin C (d) A specific storage time, a fruit pack, amount of vitamin C (e) A specific storage time, the nutritionist, amount of vitamin C

8. 4. A researcher observes that, on average, the number of divorces in cities with Major League Baseball teams is larger than in cities without Major League Baseball teams. The most plausible explanation for this observed association is that the (a) presence of a Major League Baseball team causes the number of divorces to rise. (b) high number of divorces is responsible for the presence of Major League Baseball teams. (c) association is due to the presence of a lurking variable. (d) association makes no sense, since many married couples go to the ballpark together. (e) observed association is purely coincidental. It is impossible to believe the observed association could be anything other than accidental.

9. 5. Control groups are used in experiments in order to (a) minimize the effects of variables that are not factors in the experiment on the outcome. (b) control the subjects of a study to ensure that all participate equally. (c) guarantee that someone other than the investigators, who have a vested interest in the outcome, controls how the experiment is conducted. (d) achieve a proper and uniform level of randomization. (e) reduce the variability in results.

10. 6. Which of the following statements is false
6. Which of the following statements is false? (a) Nonresponse can cause bias in surveys because nonrespondents often tend to behave differently than people who respond. (b) Non-random samples can distort the results of a survey. (c) Slight changes in the wording of questions can make a measurable difference in survey results. (d) People will sometimes answer a question differently for different interviewers. (e) Sophisticated statistical methods can always correct the results if the population you are sampling from is different from the population of interest, for example, due to undercoverage.

11. 7. An airline that wants to assess customer satisfaction chooses a random sample of 10 of its flights during a single month and asks all of the passengers on those flights to fill out a survey. This is an example of a (a) multistage sample. (b) stratified sample. (c) cluster sample. (d) simple random sample. (e) convenience sample.

12. 8. We say that the design of a study is biased if which of the following is true? (a) A racial or sexual preference is suspected. (b) Random placebos have been used. (c) Certain outcomes are systematically favored. (d) The correlation is greater than 1 or less than –1. (e) An observational study was used when an experiment would have been feasible.

13. 9. A survey is to be administered to recent graduates of a certain nursing school in order to compare the starting salaries of women and men. For a random sample of graduates, three variables are to be recorded: sex, starting salary, and area of specialization. Which of the following best describes a conclusion that can be drawn from this study? (a) Whether being female causes graduates of this nursing school to have lower (or higher) starting salaries than males. (b) Whether being female causes graduates in this sample to have lower (or higher) starting salaries than males. (c) Whether choosing certain area of specialization causes female graduates of this nursing school to have lower (or higher) starting salaries than males. (d) Whether there is an association between sex and starting salary among graduates of this nursing school. (e) Whether there is an association between sex and starting salary at all nursing schools.

14. 10. The following numbers appear in a table of random digits: A scientist will be measuring the total amount of leaf litter in a random sample (n = 5) of forest sites selected without replacement from a population of 45 sites. The sites are labeled 01, 02, , 45 and she starts at the beginning of the line of random digits and takes consecutive pairs of digits. Which of the following is correct? (a) Her sample is 38, 25, 02, 38, 22 (b) Her sample is 38, 68, 35, 02, 22 (c) Her sample is 38, 35, 27, 28, 08 (d) Her sample is 38, 65, 35, 02, 79 (e) Her sample is 38, 35, 02, 22, 40

15. 11. In order to estimate the proportion of students at a college who spend more than 2 hours per day on Facebook, a random sample of students at the college is selected and each student is interviewed. The students conducting the survey are worried that people who spend a lot of time on Facebook may be embarrassed to admit it and their responses may not be honest. What type of bias are the students conducting the survey worried about? (a) Selection bias (b) Nonresponse bias (c) Measurement bias (d) Bias due to confounding (e) There is no obvious source of bias

16. 12. To estimate the proportion of students who plan to purchase tickets to an upcoming school fundraiser, a high school decides to sample 100 students as they pick up their schedules in August. There are 2000 students at the school. Which of the following sampling plans would result in a stratified random sample? (a) Number the students from 1 to 2000 and use random numbers to select 100 students. (b) Survey the first 100 students to pick up their schedule. (c) Randomly select 100 students from a list of 950 female students at the school (d) Divide the students into those who pick up their schedules early (first 1000 students) and late (last 1000 students). Use random numbers to identify 50 from each group. (e) Select one of the first 20 students to pick up their schedule using a random number table and then select every 20th student after.

17. 13. Which of the following describes a situation in which it is reasonable to reach a cause and effect conclusion based on data from a statistical study? (a) The study is based on a random sample from a population of interest. (b) The study is observational and the sample used is not a convenience sample. (c) The study is an experiment that uses random assignment to assign volunteers to experimental conditions (treatments). (d) The study is observational and the two samples used are not convenience samples (e) It is always reasonable to reach a cause and effect conclusion based on data from a statistical study.

18. 14. In a study of shopping preferences, a sample of young adults and a sample of people over age 50 were selected. Each person was asked where he or she preferred to shop for groceries. Based on the resulting data, the investigators concluded that a higher proportion of older adults prefer to shop at chain supermarkets. Which of the following is true for this study? (a) The study is an experiment with two treatments, young and old. (b) The study is an experiment with two treatments, shopping at chain supermarkets or not shopping at chain supermarkets. (c) The study is an experiment that incorporates blocking by age. (d) Based on this study, it is reasonable to conclude that there is a cause and effect relationship between age and shopping preference. (e) None of the above is true for this study.

19. 15. Fifty-two volunteers participated in an experiment to investigate the effect of noise on reaction time. The volunteers were divided into 2 groups based on age, the youngest 26 in the “young” group and the oldest 26 in the “old” group. Each person in the young group was assigned at random to have his or her reaction time measured in a quiet room or in a noisy room. Each person in the old group was also assigned at random to the quiet room or the noisy room. Which of the following is true? (a) This experiment has a control group. (b) This experiment incorporates blocking. (c) This experiment is double blind. (d) This experiment is double blind and incorporates blocking. (e) This experiment has a control group, is double blind and incorporates blocking.

20. 16. Fifty-two volunteers participated in an experiment to investigate the effect of noise on reaction time. The volunteers were divided into 2 groups based on age, the youngest 26 in the “young” group and the oldest 26 in the “old” group. Each person in the young group was assigned at random to have his or her reaction time measured in a quiet room or in a noisy room. Each person in the old group was also assigned at random to the quiet room or the noisy room. Which of the following are treatments in this experiment? (a) Room condition (quiet or noisy) (b) Age (young or old) (c) Reaction time (d) The two groups of volunteers (e) There are no treatments in the experiment

21. 17. Researchers want to compare students at private vs
17. Researchers want to compare students at private vs. public universities with respect to how much time they spend working in a typical week. They ed a survey to 1000 students at a particular private school and to 2000 students at a particular public school. Data from the 400 private and 900 public school students who returned the survey indicated there was a significant difference in the mean hours worked per week. Which of the following does not limit the researchers ability to generalize to the 2 populations of interest? (a) There may be bias due to nonresponse (b) The two sample sizes are not equal (c) The samples were not randomly selected (d) All the students in the survey attend either one private or one public university (e) All of the above limit the researchers ability to generalize