SADC Course in Statistics Sampling design using the Paddy game (Sessions 15&16)

SADC Course in Statistics

Sampling design using the Paddy game

(Sessions 15&16)

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Learning Objectives

By the end of these sessions, you will be able

to

• utilise skills in designing your own sampling scheme to address given objectives

• collect data, analyse and present the results appropriately to demonstrate your key findings

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Paddy demonstration: Aims

• To introduce the Paddy game and show how it may be used to select a multi-stage sample

• To illustrate, via a small example, how population values can be estimated from sample values

Note: a separate handout sets out the aims of the paddy exercise and tasks that you are expected to carry out

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• Paddy is a game that has been developed to provide practice on how a sampling design may be developed and the data analysed, once collected

• The game uses an example of a survey of rice production

• Open the Paddy game on your computer by clicking on the PADDY icon

What is the Paddy Game?

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• 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.

Background information

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Farmer numbers and their acreages

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• To estimate the mean yield of rice per hectare and hence the total production of rice in the district

• to investigate the use of fertilisers and improved varieties by the farmers

• to study the relationship between these factors (fertiliser, variety) and the yield of rice.

Paddy survey objectives

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• In order to address the objectives, 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 plot covers an area of 1/80th of an acre.• The resources available allow you to visit

and collect information from 30 plots.• Yield from each harvested plot is then

measured in bushels per acre.

Crop-cutting survey process

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• 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– Village as primary sampling unit– Farmer’s field within village as the

secondary unit– Plot within field as the final stage unit

Resources

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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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The Sample in Excel

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Computing population Estimates

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Practise playing the Paddy Game

• Now practise playing the paddy game yourself using a different sampling scheme to that presented in the previous slide

• The aim here is merely to give you practice – it does not matter that the scheme is not suitable for the actual study

• You will have 15 minutes for this activity

• We will then demonstrate how the computer version can be used to draw a PPS sample

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Paddy Game with PPS sampling

Suppose the sampling scheme suggested isthe 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

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Computing population Estimates

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Now practise drawing a PPS sample.

Also read the more detailed handout regarding your tasks for the next

two practical sessions…