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# Lecture1-note - Objectives Producing data: sampling...

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1 Producing data: sampling BPS chapters 1.1, 4.1 & 8 © 2007 W. H. Freeman and Company Objectives Producing data: sampling ± Individuals and variables ± Explanatory, response and lurking variables ± Observation versus experiment ± Population versus sample ± How to sample badly ± Simple random samples ± Other sampling designs ± Caution about sample surveys ± Learning about populations from samples (inference) Individuals and variables Individuals are the objects described by a set of data. Individuals may be people, but they may also be animals or things. A variable is any characteristic of an individual. A variable can take different values for different individuals. Explanatory and response variables A response variable measures or records an outcome of a study. An explanatory variable explains changes in the response variable. Explanatory (independent) variable: number of beers Blood Alcohol as a function of Number of Beers 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 01234567891 0 Number of Beers Blood Alcohol Level (mg/ml) Response (dependent) variable: blood alcohol content x y Explanatory and response variables A response variable measures or records an outcome of a study. An explanatory variable explains changes in the response variable. Lurking variables A lurking variable is a variable not included in the study that may influence the interpretation of relationships between variables. ± Strong positive association between the number firefighters at a fire site and the amount of damage a fire does

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2 Population versus sample ± Sample : The part of the population we actually examine and for which we do have data ± A s tatistic is a variable describing a characteristic of a s ample. ± Population: The entire group of individuals in which we are interested but can’t usually assess directly ± A p arameter is a variable describing a characteristic of the p opulation. Population Sample Producing Data: Observation versus experiment Observational study: Record data on individuals without attempting to influence the responses. We typically cannot prove anything this way.
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## This note was uploaded on 04/26/2008 for the course BIOL 7 taught by Professor Luo during the Fall '07 term at UC Irvine.

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Lecture1-note - Objectives Producing data: sampling...

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