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Multistage Sampling

Module 3

Session 9

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Session Objectives

To introduce Multistage sampling

To help participants appreciate when to apply multi-stage sampling

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Multi-Stage Sampling Design

Most commonly used sampling design in practice

Involves more than one stage of sampling and/or a combination of two or more sampling designs

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Why apply multi-stage sampling

Structure of the population

Size of population (large)

Fund available for the survey

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Examples of multi-stage sampling

1. A Systematic sample of households within Enumeration Areas (EAs) within Districts

Districts – Strata – 1st Stage EAs- Clusters- 2nd Stage Households -3rd Stage

• Within each District take a sample of EAs• Within each EAs, take a sample of h’holds• Within each household, sample 2 individuals

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Cont’d

2. Determine from students at a university their opinion of the university.

Stratify students according to their Faculty (Science, etc.) (strata 1st )

Take simple random sample of courses in each of these Faculties (clusters 2nd )

From each course take a random sample of students.

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Sampling and Analysis issues using

the Paddy Game

Module 3

Session 9(b)

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Session Objectives

To introduce basic sampling concepts using the Paddy game

To demonstrate how to select a sample from a population

To demonstrate how population values can be estimated from samples

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What is Paddy?

Paddy is a game that has been developed to demonstrate how to design and analyse survey data

The game uses an example of a survey of rice production

Open the paddy game on your computer by clicking on the PADDY icon.

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Background Information

In a small district there are: 10 villages With a total of 160 farmers Each with one field in which to grow rice

A census has been undertaken and the acreage cultivated by each farmer is known.

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Number of Farmers & Acreage - by Village

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Aim of the Survey

The main aim of the survey is to estimate the mean yield of rice per hectare and hence the total production of rice in the district

In order to do this you will carry out a crop cutting survey. This is a survey where you visit fields, harvest the crop from one or more plots and measure the yield

A further objective is to investigate the use of fertiliser and varieties by the farmers

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Resources

The resources available allow you to visit and collect information from 30 plots.

A plot covers an area of 1/80th of an acre. Yield from each plot harvested is then

measured in bushels per acre.

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Resources

Transport costs allow your survey team to visit a maximum of 5 villages, although you might decide to visit less than 5.

These costs dictate that the survey should use a multistage sampling design

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Resources

The game gives you the possibility of three levels: Villages Farmers within Village Plots within farmers.

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Pilot Run We begin with a pilot run to give you familiarity with

the Paddy game The Paddy game has been installed on your

computers The sampling scheme suggested is the following:

Select 2 villages using simple random sampling From each village select 3 fields, again with simple

random sampling From each field, select 1 plot at random for harvesting

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Designing the Sampling scheme

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Designing the Sampling Scheme- Selecting fields in village 6 -

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Designing the Sampling Scheme- Selecting fields in village 7 -

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The Sample

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Probability Proportional to Size (PPS) Sampling using the Paddy Game

Module 3

Session 9(c)

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Session Objectives

To demonstrate how to select a sample from a population using PPS

To demonstrate how population values can be estimated from samples

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Pilot Run

Suppose the sampling scheme suggested is the following:

Select 2 villages using PPS sampling where the sample depends on the number of farmers in the village

From each village select 3 fields, with simple random sampling

From each field, select 1 plot at random for harvesting

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Designing the Sampling scheme

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Designing the Sampling scheme

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Selecting fields for Village 6

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Selecting fields for Village 7

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The Sample