Sampling design using
the Paddy game
(Sessions 15&16)
SADC Course in Statistics
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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What is the Paddy Game?
• 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
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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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Farmer numbers and their acreages
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Paddy survey objectives
• 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.
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Crop-cutting survey process
• 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.
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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
– Village as primary sampling unit
– Farmer’s field within village as the
secondary unit
– Plot within field as the final stage unit
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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 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
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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…
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