andrew_gelman_stats andrew_gelman_stats-2012 andrew_gelman_stats-2012-1348 knowledge-graph by maker-knowledge-mining
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Introduction: 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution to question 16 From yesterday : 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution: x is 1 if the respondent is an unemployed man, 0 otherwise. y is 1 if the respondent is an unemployed man and supports the rebels, 0 otherwise. The estimate is y.bar/x.bar [typo fixed], the standard error is (1/x.bar)*(1/sqrt(n))*s.z, whe
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1 In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare. [sent-2, score-1.73]
2 ” The goal is to estimate the effect of the wording on the proportion of Yes responses. [sent-3, score-0.67]
3 How large must n be for the effect to be estimated within a standard error of 5 percentage points? [sent-4, score-0.901]
4 Solution to question 16 From yesterday : 16. [sent-5, score-0.113]
5 You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. [sent-6, score-1.987]
6 Express this as a ratio estimation problem, where goal is to estimate Y. [sent-7, score-0.535]
7 Give the estimate and standard error for the percentage of unemployed men who support the rebels. [sent-11, score-1.741]
8 Solution: x is 1 if the respondent is an unemployed man, 0 otherwise. [sent-12, score-0.769]
9 y is 1 if the respondent is an unemployed man and supports the rebels, 0 otherwise. [sent-13, score-1.038]
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same-blog 1 1.0 1348 andrew gelman stats-2012-05-27-Question 17 of my final exam for Design and Analysis of Sample Surveys
Introduction: 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution to question 16 From yesterday : 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution: x is 1 if the respondent is an unemployed man, 0 otherwise. y is 1 if the respondent is an unemployed man and supports the rebels, 0 otherwise. The estimate is y.bar/x.bar [typo fixed], the standard error is (1/x.bar)*(1/sqrt(n))*s.z, whe
2 0.43169364 1349 andrew gelman stats-2012-05-28-Question 18 of my final exam for Design and Analysis of Sample Surveys
Introduction: 18. A survey is taken of 100 undergraduates, 100 graduate students, and 100 continuing education students at a university. Assume a simple random sample within each group. Each student is asked to rate his or her satisfaction (on a 1–10 scale) with his or her experiences. Write the estimate and standard error of the average satisfaction of all the students at the university. Introduce notation as necessary for all the information needed to solve the problem. Solution to question 17 From yesterday : 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution: se is sqrt(.5*.5/(n/2)+.5*.5/(n/2)) = 1/sqrt(n). Solve 1/sqrt(n) = .05, you get n = (1/.05)^2 = 400.
3 0.34205213 1345 andrew gelman stats-2012-05-26-Question 16 of my final exam for Design and Analysis of Sample Surveys
Introduction: 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution to question 15 From yesterday : 15. A researcher conducts a random-digit-dial survey of individuals and married couples. The design is as follows: if only one person lives in a household, he or she is interviewed. If there are multiple adults in the household, one is selected at random: he or she is interviewed and, if he or she is married to one of the other adults in the household, the spouse is interviewed as well. Come up with a scheme for inverse-probability weights (ignoring nonresponse and assuming there is exactly one phone line per household). Solution: Your probability of being selected is proportional to: (1/(#adults in yo
4 0.17151834 1341 andrew gelman stats-2012-05-24-Question 14 of my final exam for Design and Analysis of Sample Surveys
Introduction: 14. A public health survey of elderly Americans includes many questions, including “How many hours per week did you exercise in your most active years as a young adult?” and also several questions about current mobility and health status. Response rates are high for the questions about recent activities and status, but there is a lot of nonresponse for the question on past activity. You are considering imputing the missing values on the question, “How many hours per week did you exercise in your most active years as a young adult?” Which of the following statements are basically correct? (Indicate all that apply.) (a) If done reasonably well, imputation is preferred to available-case and complete-case analysis. (b) If you do impute, you should also present the available-case and complete-case analysis and analyze how the imputed estimates differ. (c) It is OK to include current health status variables as predictors in a model imputing past activities: anything that adds informati
5 0.16002716 1315 andrew gelman stats-2012-05-12-Question 2 of my final exam for Design and Analysis of Sample Surveys
Introduction: 2. Which of the following are useful goals in a pilot study? (Indicate all that apply.) (a) You can search for statistical significance, then from that decide what to look for in a confirmatory analysis of your full dataset. (b) You can see if you find statistical significance in a pre-chosen comparison of interest. (c) You can examine the direction (positive or negative, even if not statistically significant) of comparisons of interest. (d) With a small sample size, you cannot hope to learn anything conclusive, but you can get a crude estimate of effect size and standard deviation which will be useful in a power analysis to help you decide how large your full study needs to be. (e) You can talk with survey respondents and get a sense of how they perceived your questions. (f) You get a chance to learn about practical difficulties with sampling, nonresponse, and question wording. (g) You can check if your sample is approximately representative of your population. Soluti
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Introduction: 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution to question 16 From yesterday : 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution: x is 1 if the respondent is an unemployed man, 0 otherwise. y is 1 if the respondent is an unemployed man and supports the rebels, 0 otherwise. The estimate is y.bar/x.bar [typo fixed], the standard error is (1/x.bar)*(1/sqrt(n))*s.z, whe
2 0.9070459 1361 andrew gelman stats-2012-06-02-Question 23 of my final exam for Design and Analysis of Sample Surveys
Introduction: 23. Suppose you are conducting a survey in which people are asked about their health behaviors (how often they wash their hands, how often they go to the doctor, etc.). There is a concern that different interviewers will get different sorts of responses—that is, there may be important interviewer effects. Describe (in two sentences) how you could estimate the interviewer effects within your survey. Can the interviewer effects create problems of reliability of the survey responses? Explain (in one sentence). Can the interviewer effects create problems of validity of the survey responses? Explain (in one sentence). Solution to question 22 From yesterday : 22. A supermarket chain has 100 equally-sized stores. It is desired to estimate the proportion of vegetables that spoil before being sold. Three stores are selected at random and are checked: the percent of spoiled vegetables are 3%, 5%, and 10% in the three stores. Give an estimate and standard error for the percentage of spo
3 0.8901521 1349 andrew gelman stats-2012-05-28-Question 18 of my final exam for Design and Analysis of Sample Surveys
Introduction: 18. A survey is taken of 100 undergraduates, 100 graduate students, and 100 continuing education students at a university. Assume a simple random sample within each group. Each student is asked to rate his or her satisfaction (on a 1–10 scale) with his or her experiences. Write the estimate and standard error of the average satisfaction of all the students at the university. Introduce notation as necessary for all the information needed to solve the problem. Solution to question 17 From yesterday : 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution: se is sqrt(.5*.5/(n/2)+.5*.5/(n/2)) = 1/sqrt(n). Solve 1/sqrt(n) = .05, you get n = (1/.05)^2 = 400.
4 0.86431032 1345 andrew gelman stats-2012-05-26-Question 16 of my final exam for Design and Analysis of Sample Surveys
Introduction: 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution to question 15 From yesterday : 15. A researcher conducts a random-digit-dial survey of individuals and married couples. The design is as follows: if only one person lives in a household, he or she is interviewed. If there are multiple adults in the household, one is selected at random: he or she is interviewed and, if he or she is married to one of the other adults in the household, the spouse is interviewed as well. Come up with a scheme for inverse-probability weights (ignoring nonresponse and assuming there is exactly one phone line per household). Solution: Your probability of being selected is proportional to: (1/(#adults in yo
5 0.84515005 1358 andrew gelman stats-2012-06-01-Question 22 of my final exam for Design and Analysis of Sample Surveys
Introduction: 22. A supermarket chain has 100 equally-sized stores. It is desired to estimate the proportion of vegetables that spoil before being sold. Three stores are selected at random and are checked: the percent of spoiled vegetables are 3%, 5%, and 10% in the three stores. Give an estimate and standard error for the percentage of spoiled vegetables for the entire chain. Solution to question 21 From yesterday : 21. A country is divided into three regions with populations of 2 million, 2 million, and 0.5 million, respectively. A survey is done asking about foreign policy opinions. Somebody proposes taking a sample of 50 people from each reason. Give a reason why this non-proportional sample would not usually be done, and also a reason why it might actually be a good idea. Solution: Nonproportional sampling is usually avoided because it makes the analysis more complicated and it results in a higher standard error for estimates of the general population. It might be a good idea her
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Introduction: 17. In a survey of n people, half are asked if they support “the health care law recently passed by Congress” and half are asked if they support “the law known as Obamacare.” The goal is to estimate the effect of the wording on the proportion of Yes responses. How large must n be for the effect to be estimated within a standard error of 5 percentage points? Solution to question 16 From yesterday : 16. You are doing a survey in a war-torn country to estimate what percentage of unemployed men support the rebels in a civil war. Express this as a ratio estimation problem, where goal is to estimate Y.bar/X.bar. What are x and y here? Give the estimate and standard error for the percentage of unemployed men who support the rebels. Solution: x is 1 if the respondent is an unemployed man, 0 otherwise. y is 1 if the respondent is an unemployed man and supports the rebels, 0 otherwise. The estimate is y.bar/x.bar [typo fixed], the standard error is (1/x.bar)*(1/sqrt(n))*s.z, whe
2 0.95742261 1282 andrew gelman stats-2012-04-26-Bad news about (some) statisticians
Introduction: Sociologist Fabio Rojas reports on “a conversation I [Rojas] have had a few times with statisticians”: Rojas: “What does your research tell us about a sample of, say, a few hundred cases?” Statistician: “That’s not important. My result works as n–> 00.” Rojas: “Sure, that’s a fine mathematical result, but I have to estimate the model with, like, totally finite data. I need inference, not limits. Maybe the estimate doesn’t work out so well for small n.” Statistician: “Sure, but if you have a few million cases, it’ll work in the limit.” Rojas: “Whoa. Have you ever collected, like, real world network data? A million cases is hard to get.” The conversation continues in this frustrating vein. Rojas writes: This illustrates a fundamental issue in statistics (and other sciences). One you formalize a model and work mathematically, you are tempted to focus on what is mathematically interesting instead of the underlying problem motivating the science. . . . We have the sam
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5 0.95226485 1050 andrew gelman stats-2011-12-10-Presenting at the econ seminar
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