t11 - 1 Geography 231 Introduction to Geospatial Methods...

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Unformatted text preview: 1 Geography 231 Introduction to Geospatial Methods Topic 11: Samples and Sampling Goals To understand the role of sampling in geographic analysis Sampling strategies Simple random sampling Stratified random sampling Non-random sampling (systematic & selective ) Sampling units: How many do you need? Sampling units: How many do you need? 2 Samples and Populations Population: the universe of all individuals/entities In order to measure them all, we would need to conduct a census , and this often not feasible Sample: a subset or portion of the population upon which measurements are obtained Hopefully, the sample represents the population! The Role of Sampling Sampling helps us answer a number of difficult questions 1. How large should the sample be? 2. How/where should the samples be chosen? 3. How much reliability will we have in results based on this sample? All of these revolve around the fact that we normally can’t conduct a census of an entire population! 3 Sampling Units Sampling units: the individual items in a sample, and the basic entity upon which observations are made May be discrete entities (e.g. people, households, cities, etc) or areas (e.g. quadrats, strips, plots, etc) Must be explicitly defined! Sampling units must be selected to match the scale of the information desired E.g.: household income Æ households Personal income Æ individual people Sampling Strategies There are many techniques designed to help achieve a sample that is ‘representative’ of the population We will consider four of them: simple random, systematic, stratified random, and non-random The major issue to avoid is...
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This note was uploaded on 02/04/2010 for the course GEOG 158 taught by Professor Dobson,j during the Spring '08 term at Kansas.

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t11 - 1 Geography 231 Introduction to Geospatial Methods...

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