Chap5-Data-Collection-and-Sampling

Chap5-Data-Collection-and-Sampling - 1 CHAPTER 5: DATA...

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Unformatted text preview: 1 CHAPTER 5: DATA COLLECTION AND SAMPLING Stats & Prob. for Bus. Mgmt (Stat1100) Jochem Data Collection & Sampling b Overview b 1. Collection Methods b 2. Sampling Methods . Sample Size 2 b 3. Sample Size b 4. Sampling Errors & Nonsampling Errors Data Collection & Sampling b 1. Collection Methods 3 Methods: b 1.1 Direct observation .2 Experiments 3 b 1.2 Experiments b 1.3 Surveys Data Collection & Sampling b 1. Collection Methods b 1.1 Direct observation s Q: “ Does aspirin reduce the risk of heart attack?” s Observe the number of heart attacks within the last 2 years 4 among a group of aspirin-takers and one that does not take aspirin and use some statistical technique (Chaps 13ff.) to see if there is a significant difference. s Drawback to this method: s Does the aspirin really reduce heart attack, or is it that more health-conscious/educated/richer people (who are less prone to heart attacks) take more aspirin? Data Collection & Sampling b 1. Collection Methods b 1.1 Direct observation s Problems with direct observations: s 1. Omitted Variable Bias 3 ctor (e.g., income) drives the observed pattern: It is not the 5 A 3 rd factor (e.g., income) drives the observed pattern: It is not the aspirin leading to fewer heart attacks, but instead higher-income individuals use more aspirin and have overall more healthy lives, thereby lowering heart attack risk. Data Collection & Sampling b 1. Collection Methods b 1.1 Direct observation s Problems with direct observations: s 1. Omitted Variable Bias 3 d ctor (e.g., income) drives the observed pattern: It is not the 6 A 3 rd factor (e.g., income) drives the observed pattern: It is not the aspirin leading to fewer heart attacks, but instead higher-income individuals use more aspirin and have overall more healthy lives, thereby lowering heart attack risk. s 2. Self-Selection Health-conscious people (who use more aspirin and have a lower risk of heart attack) are more likely to participate in your study. Data Collection & Sampling b 1. Collection Methods b 1.1 Direct observation s Problems with direct observations: s 1. Omitted Variable Bias 3 ctor (e.g., income) drives the observed pattern: It is not the 7 A 3 rd factor (e.g., income) drives the observed pattern: It is not the aspirin leading to fewer heart attacks, but instead higher-income individuals use more aspirin and have overall more healthy lives, thereby lowering heart attack risk. s 2. Self-Selection Health-conscious people (who use more aspirin and have a lower risk of heart attack) are more likely to participate in your study. s 3. Reverse Causality It is not aspirin that leads to fewer heart attacks, but a lower risk of a heart attack is correlated with having more headaches (and therefore with taking more aspirin)....
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This note was uploaded on 03/26/2012 for the course STAT 1100 taught by Professor Chiappetta during the Spring '08 term at Pittsburgh.

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Chap5-Data-Collection-and-Sampling - 1 CHAPTER 5: DATA...

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