Class 1. b. Sampling a total of 100 Californians, where individuals are randomly selected from each major ethnic group.

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1 What you need to know: Class 1 Sampling Study design The goal and importance of sampling methods Bias Sampling frame Volunteer sample Convenience sample Systematic sample Volunteer response Non-response Probability sampling plan o Simple random sample (SRS) o Cluster sample o Stratified sample o Multistage sample Observational study (prospective and retrospective) Sample survey Experiment What a factor is in an experiment What we mean by Treatment, Treatment group, and Control group What are the subjects in an experiment What is a randomized controlled experiment What the difference is between random sampling and random assignment What we mean by blind and double blind experiments What a placebo is, and the placebo effect What the experimenter effect is That the most reliable way to determine whether the explanatory variable is actually causing changes in the response variable is to carry out a randomized controlled experiment. that blind and double-blind experiments should be used where possible The pitfalls in experimentation Lack of realism o Non-compliance o Impractical and unethical experiments Experiments with more than one factor Block design and Matched pair design Sample surveys o Wording of question o Ordering of questions o Type of questions asked quantitative variable/categorical variable distribution of a variable numerical displays for one categorical variable: category counts and percents graphical displays for one categorical variable: bar charts and pie charts how to create and describe graphical displays for one quantitative variable o dotplots o histograms (frequency and relative frequency histograms) o stemplots 1. What kind of sampling design is used in these examples? a. Sampling 100 male and 150 female VC students b. Sampling a total of 100 Californians, where individuals are randomly selected from each major ethnic group. c. Choosing people in both urban and rural areas, from different income groups within the urban and rural areas, and then individuals of different ethnicities within those strata. d. Sampling 25 employees from a company, where every possible set of 25 employees has the same chance of being the sample actually taken.

2 e. Selecting all the students chosen from a few randomly selected elementary schools in the district f. Choosing 25 randomly selected cookies in a bakery g. Sampling all the cookies from a few randomly selected bags of cookies h. The bakery makes four types of cookies: chocolate chip cookies, sugar cookies, oatmeal raisin cookies and macadamia nut cookies. You choose five from each type. i. Sampling every fifth cookie on the tray 2. Let s assume I have a crazy idea: I will give an A as a final grade to a few randomly selected students in this class. I have a few ways to select these lucky students. Identify my sampling methods for each case: a. I randomly pick 5 students from the roster b. I randomly pick two rows in the class and give an A to all students in those rows c. I randomly pick 5 females and 5 males d. I start with the third person in the first row and count by 5 s to select the lucky students e. I randomly select 1 freshman, 1 sophomore, 1 junior, and 1 senior from the female students, and 1 freshman, 1 sophomore, 1 junior, and 1 senior from the male students f. I randomly select one class year (freshman, sophomore, junior, or senior) and give all of those students A s. 3. For the following situations identify the sampling method, including whether or not random sampling was employed, and potential sources of bias or any other problems. a. An online magazine asks its readers to vote on whether they thought that a 4-day workweek would hurt the economy. b. Researchers waited outside a bar and asked every 5 th person who came out of the bar whether he or she thought drinking and driving was a serious problem. c. Researchers called 1000 randomly selected phone numbers to ask the callers opinions about radio stations. 4. For the following situations identify whether it was an observational study (prospective or retrospective) or an experiment. a. Researchers examined health records of a 1000 males and found that men who died of prostate cancer tended to be shorter than men who did not.

3 b. Researchers studied the effects of omega-3 fats from fish oil on 30 people with bipolar disorder. They randomly assigned 15 people to one of three groups: (1) normal dose of omega-3 fats pills (5g/day), (2) high dose of omega-3 fats pills (10 g/day), (3) placebo (a fake pill). c. An artisan wants to create pottery that has the appearance of age. She prepares several samples of clay with four different glazes and test fires them at three different temperature settings. 5. You need to gather students opinions about parking for students on campus. It s not practical to ask all the students at VC. a. Give an example of a way to choose a sample of students that is a poor design because it depends on voluntary response. b. Give another example that doesn t use voluntary response but is still a bad way of sampling that doesn t use voluntary response. c. Give four correct ways of sampling. That is, describe four different unbiased methods for sampling students opinions.

4 6. What is the difference between an observational study and an experiment? 7. A food company assesses the nutritional quality of a new instant breakfast product by feeding it to newly weaned male white rats. In this experiment they used 30 rats, and compared the new product with the standard products. After 28 days they measured the rats weight gain. a. What is the explanatory variable (factor)? b. What is the response variable? c. Use a diagram to outline the design of a randomized comparative experiment. (make sure you indicate the size of the treatment groups and the response variable) 8. We have a population of 200 people. We would like to study the effect that a pill has on the hours of sleep that a person gets. a. Do we need an experiment or an observational study? Explain. b. What features should our experiment have? c. Draw the outline of the experiment (make sure you indicate the size of the treatment groups and the response variable).

5 9. A pharmaceutical company has developed a new pain-relief medication for arthritis. Sixty patients suffering from arthritis and needing pain relief are available. Each patient will be treated and asked an hour later, About what percentage of your pain has gone away? a. Why should this company not simply administer the new drug and record the patients responses? b. Outline the design of an experiment to compare the drug s effectiveness with that of aspirin and of a placebo. c. Should patients be told which drug they are receiving? How would this knowledge probably affect their reaction? d. Should this experiment be double-blinded also? Explain. e. Preliminary work suggests that calcium may be effective and that the effect may be greater for black men than for white men. Use a diagram to outline an appropriate experiment. Explain where you use randomization in this design.

6 For each of the following variables, indicate whether it is a quantitative or a qualitative (categorical) variable. 1. height 2. armspan 3. ratio of height to armspan 4. time spent sleeping last night 5. whether or not the individual went to sleep before midnight last night 6. month of birth 7. numerical score (out of a possible 100 points) on the first exam in this class 8. whether or not the individual scores at least 70 points on the first exam in this class 9. distance from home 10. whether the individual has a cell phone 11. whether the person has sent at least one message in the last 72 hours 12. the number of letters on the last name 13. whether a spun penny lands heads or tails 14. the color of a Reese s Pieces candy 15. the number of calories in a fast food sandwich 16. the life expectancy of a nation 17. whether an American household owns a cat or does not own a cat 18. the year in which a college was founded 19. for whom an American voted in the 1996 Presidential election 20. whether or not a newborn baby tests HIVpositive 21. the running time of an Alfred Hitchcock movie 22. the age of an American penny 23. the weight of an automobile 24. whether an automobile is foreign or domestic to the U.S. 25. the classification of an automobile as small, midsize, or large 26. whether or not an applicant for graduate school is accepted 27. the occupational background of a Civil War general 28. whether or not an American child lives with both parents 29. whether a college student has abstained form the use of alcohol for the past month 30. a sport s injury rate per 1000 participants 31. whether or not a participant in a sport suffers an injury in a given year 32. a state s rate of automobile thefts per 1000 residents 33. the airfare to a selected city from Los Angeles 34. the average low temperature in January for a city 35. the age of a bride on her wedding day Qualitative (Categorical) Data