chapter4 - CHAPTER 4: PRODUCING DATA 4.1 Introduction How...

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CHAPTER 4: PRODUCING DATA 4.1 Introduction How to verify the following statements? 1. Pet owners are less likely to die of coronary heart disease. 2. Regular large doses of vitamin C reduce the chance of getting a common cold. Response variable – a variable whose changes we wish to study; an outcome or result. Explanatory variable - a variable that explains or causes changes in the response variable. Example: We want to know whether people who exercise regularly are less likely to catch colds. Explanatory variable =status (exercise, no exercise), Response variable = number of colds in a specified period. Study Designs Observational studies Experiments 1
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Observational study – observes individuals and measures variables of interest but does not attempt influence the responses Experiment – deliberately imposes some action on individuals in order to observe their responses. Example: Pet ownership and CHD survival Each of 92 patients with coronary heart disease (CHD) was classified as having a pet or not and by whether they survived for 1 year. Pet Ownership Patient No Yes Alive 28 50 Dead 11 3 Survival rate among patients with pets is 50/53 or 94%, whereas survival rate among patients without pets is 28/39 or 72%. Is higher survival rate among patients with pets due to the pet ownership? Group 1 (pet) Survival rate Comparison Survival rate Group 2 (no pet) Explanatory variable: Pet ownership (pet, no pet), Response variable: Survival (yes, no) 2
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Pet ownership Personality L i f e s t y l e Survival Diet Other A lurking variable is a variable that has an important effect on the relationship among the variables in a study but is not included among the variables studied. Two variables are confounded when their effects on a response variable cannot be distinguished from each other. The confounded variables may be either explanatory variables or lurking variables. Example: Smoking during Pregnancy and Child’s IQ Study: Smoking May Lower Kids’ IQs Rochester, N.Y. – Women who light up while pregnant could be dooming their babies to lower IQ’s, according to a study released Thursday. Children age 4 whose mothers smoked 10 or more cigarettes a day during pregnancy scored about 9
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chapter4 - CHAPTER 4: PRODUCING DATA 4.1 Introduction How...

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