To the Woods:
a sampling game
(Sessions 08 & 09)
SADC Course in Statistics
Learning Objectives
By the end of these sessions, you will
• put into practice sampling concepts learnt in
the previous sessions
• have skills in drawing a simple and stratified
sample from a realistic scenario
• appreciate the benefits of stratification in
comparison to simple random sampling
• acquire an appreciation of how a population
ratio may be estimated
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Introducing “To the Woods”
• This sampling game concerns trees in a
given forest.
• A small survey is done with the objective of
– estimating the total number of trees in the
forest
– estimating the proportion of large trees in
the forest
• Both “hand” and “computer” versions of
this game are available. You will need to
decide which to use.
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Description of forest
• The area of forest from which the sample is
to be taken is conveniently rectangular.
• It consists of one region on each side of
the River.
• Within each region it is possible to count
the number of trees in any 50m × 50m
strip.
• There are altogether 168 such strips, 96 to
the West of the river and 72 to the East.
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Map showing strips of forest
Highlighted (yellow) strips show an example
of selecting 14 strips from the forest.
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Sampling exercise
• Attached handout describes two possible
sampling schemes you might adopt in
sampling the forest in order to address the
two stated objectives.
• The game should be played in pairs, doing
both scheme A and scheme B.
• Both in the pair should jointly analyse data
from each scheme.
• The results from the two schemes should
then be compared.
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Time allocation
• There will be three sessions relating to this
sampling game.
• Your work will spread over two sessions.
• You should aim to complete all questions,
including those posed at the end.
• The third session will be a discussion, using
one set of results.
• There will also be a discussion relating to
other issues, e.g. ratio estimation and poststratification.
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Practical work on “To the Woods”
game follows…
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