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Lecture 35 Today’s lecture will review key material from the first half of the semester. We will discuss questions similar to those you are likely to find on the final exam.

1.The average causal effect of dieting on body weight in a population is… A.the difference in average body weight between those in the population who diet and those in the population who do not diet B.the average weight in the population if everyone dieted, minus the average weight if no one dieted C.the average drop in weight that you would observe if all non-dieters went on a diet D.the average increase in weight that you would observe if all dieters stopped dieting

2.An education researcher wants to investigate differences in math achievement between students in local public and Catholic schools in Philadelphia. She obtains a list of all 5 th graders enrolled in public schools and all 5 th graders enrolled in Catholic schools. Then she randomly samples 100 students from each list and gives them a math achievement test. This is an example of: A.systematic sampling B.cluster sampling C.stratified sampling D.a matched-pair design

3. Which of the following is not a key advantage of a randomized experiment over an observational study? A.Randomized experiments allow us to obtain unbiased estimates of average causal effects. B.Randomized experiments eliminate confounding. C.Randomized experiments eliminate interactions. D.In a randomized experiment, there are no systematic differences between the groups receiving the different treatments

4. A pharmaceutical company runs a clinical trial to test a new drug for treating schizophrenia. They randomly assign patients to receive either the drug or a placebo. On average, patients who receive the drug showed greater improvement than those who received the placebo. Moreover, the drug seemed to be more effective in helping patients whose initial symptoms were very severe than patients who were not as severe. The latter is an example of A.confounding B.interaction C.Hawthorne effect D.correlation, as opposed to causation

5.It is often said that “correlation does not imply causation.” Remembering this is crucial when we try to interpret the results of A.surveys of all kinds B.randomized experiments of all kinds C.observational studies of all kinds D.studies with small sample size

6.Which of the following is not a common rationale for using a randomized block design instead of a completely randomized design? A.Using randomized blocks ensures that the treatment groups will be balanced with respect to important characteristics. B.Randomized block designs tend to give more precise estimates of the treatment effect. C.Randomized block designs reduce the possibility that, just by chance, the subjects in one treatment group will be very different from the subjects in another treatment group. D.Randomized block designs eliminate confounding.

7.Suppose the heights of 4 year-old boys are approximately normally distributed in the population with a mean of 40.4 inches and a SD of 1.5 inches. A doctor says that your 4 year-old brother is “at the 75 th percentile of the height distribution for his age.” About how tall is he? A (.67 × 1.5) inches B.40.4 – (.75 × 1.5) inches C.(75 – 40.4) / 1.5 inches D.(67 – 40.4) / 1.5 inches

8.In a sample of adult women, a linear regression of Y = weight (pounds) on X = height (inches) yields the following equation: A.If a woman is 62 inches tall, her predicted weight is – (3.45 × 62) pounds B.Height and weight are positively correlated. C.The intercept is not a meaningful prediction. D.Weight is the explanatory variable and height is the response. Y = – X Which of the following statements is false?

9.Examine the boxplot below. Which of the following statements is wrong? A.The lower quartile is a little less than 90. B.The interquartile range is about 15. C.The largest observation is about 130. D.The distribution looks symmetric.

10. If systolic blood pressure is normally distributed with mean 125 and standard deviation 25, about what percentage of the population has systolic pressure above 150? A.5% B.9% C.16% D.32%

11. A Stat 100 instructor gives a very easy quiz. Students’ scores (out of 10 points) are shown below. (The zero scores are for students who didn’t come to class.) A.The median, mode and maximum are equal. B.The interquartile range is zero. C.The standard deviation is zero. D.The mean is less than the median Which of the following statements is false?

12. You are hired by the IRS to analyze data from a sample of federal income tax returns for What correlation would you expect to find between X = income and Y = taxes paid? A.positive but not 1.0 B.near zero C.less than zero D.close to -1.0