introduction to sampling : censuses vs. sample surveys

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1 Introduction to Sampling : Censuses vs. Sample Surveys Module 3 Session 4

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Introduction to Sampling : Censuses vs. Sample Surveys. Module 3 Session 4. Session Objectives. Distinguish between censuses and sample surveys Demonstrate the linkages between censuses and surveys Discuss the challenges of conducting censuses and large scale surveys in Uganda - PowerPoint PPT Presentation

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Page 1: Introduction to Sampling : Censuses vs.  Sample Surveys

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Introduction to Sampling: Censuses vs.

Sample Surveys

Module 3Session 4

Page 2: Introduction to Sampling : Censuses vs.  Sample Surveys

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Session Objectives Distinguish between censuses and sample surveys Demonstrate the linkages between censuses and

surveys Discuss the challenges of conducting censuses and

large scale surveys in Uganda Distinguish between random and non random samples Identify the types and/or sources of errors in censuses

and surveys Discuss how errors can be minimised in censuses and

surveys

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Reminder of Definitions Population: totality of all units of interest Sample: part/subset of the population Censuses: inquiries that cover the whole population eg.

Uganda Population and Housing Census, CIS, EMIS, HMIS, LOGICS, etc

Sample surveys are inquiries that cover part/subset of the population eg. UDHS, UNHS, NSDS, etc

Sampling Frame: list of distinct and distinguishable units in the population of interest; beginning step in almost all random sampling schemes, e.g. numbers written on households before the census night

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Other Definitions Defacto census- covers all persons found

within the borders of a particular territory/country at a particular point in time-census night

Dejure census-tallies people according to their regular or legal residence

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Sampling Frames Sources

Administrative records-eg Hospital records Birth and Death Registers LC lists Voters’ register School registers etc

Construct your own

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Disadvantages of various sources of sampling frames

Administrative records may not be up to date

Constructing your own may be too costly especially in large scale surveys

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Role of censuses in Uganda Provide benchmark data for monitoring,

planning and policy formulation eg we need data for UPE monitoring, poverty monitoring Election monitoring Resource allocation

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Role of censuses in Uganda (cont.) Provide small area statistics - basic data

disaggregated to the lowest administrative unit e.g we use census data to know the number of people in each village, sub county and district for planning purposes

Show the actual status of the various indicators

Health indicators-mortality, disease prevalence

Fertility trends, population growth rate

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Linkages between censuses and sample surveys Sample surveys can be used as a substitute for

censuses Sample surveys can be used to supplement

census data Sample surveys can be used to pretest census

materials, procedures and methods Censuses are used as a basis for surveys

conducted between censuses Sample surveys can be used to monitor census

results

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Challenges of Conducting Censuses and Large Scale Sample Surveys Challenges of Surveys and Censuses Mubiru

James.ppt

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Types of Samples There two types of samples:

Random and Non random samples

Random samples are those whose composition is not influenced by the sampler

Non Random samples are those whose composition is influenced by the sampler

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Advantages of Random Samples Objective and hence inferences based on

them are reliable

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Disadvantages of Random Samples Costly to select Need skilled manpower to get a random

sample For some surveys, random sampling may not

be the best because the sample may not provide the required data.

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Advantages of Non Random Samples Easy and cheap to select since selection and

substitution can be done at will Since they are done at will, the data needed

can be easily obtained

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Disadvantages of Non Random Samples Subjective and hence inferences based on

them are biased Sampling errors can not be estimated

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Types of Errors There are two types of errors, namely:

Sampling errors Non sampling errors

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Sampling Errors/Biases Sampling errors are absent in censuses Their causes include:

Use of defective sampling frame Use of defective sampling procedures Use of an estimation method that does not

correspond to the sampling design

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Non Sampling Errors Non sampling errors occur both in censuses

and sample surveys but are more pronounced in censuses

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Sources of Non sampling Errors Defective sampling frames resulting into

coverage errors Under coverage Over coverage

Conceptual problems Physical environment Inadequacy of enumerators and supervisors

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Sources continued Language problems – translation Problems of measurement Response problems Non response problems Poor cartographic work Poorly designed questionnaires/instruments Poorly trained enumerators/supervisors Unqualified enumerators/supervisors

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How Errors can be Minimised Supervision Training Use of the appropriate estimation method Publicity of the survey Testing the survey instruments

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Sampling in the Research Process Problem Objectives Hypotheses Methodology

Data Sources Target population

Census or sample? If sample?

What is the sampling design?