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TECHNIQUES of SAMPLING
Choosing from among a larger population
Training Handout
How to go about selecting a small number to study as representative of a larger number
Whenever you want to say something
about a selected population, you may not be able to observe every person,
or every action, in that population.
You select part of the whole, which
you call your sample, on which to make specific observations, so that you
can make general statements about the whole or population.
Henslin, for example,
wanted to make observations about homeless people.
His method was participant observation.
He wanted to live with them and to
experience what they experienced, and to find out what they themselves
thought about the meanings of what they were doing.
He could not live with more than
one homeless group at a time, so his sample consisted of only one community
among the thousands that exist throughout North America and the rest of
the world.
If we knew for sure that every homeless
community was radically different from every other one, then the validity
of his findings would be very low.
If we believe, as we do, that there
are many similarities between those communities, his validity would be
very high, much higher, for example, than if he went around with a clipboard
asking questions from a questionnaire.
(See that the method and the sampling
technique are not as unrelated as one might first imagine both in combination
contribute to the level of validity).
Henslin gives an example of a population
being all the students of a university, and a sample being those interviewed
with a questionnaire.
How do you choose that sample?
Do you ask every fifth
person walking down a particular hallway?
Will that bias your sample towards
students taking those subjects taught in the rooms
in that hallway?
Would that bias affect the results?
If you were asking questions where
there might be significantly different answers from students taking one
subject, rather than another, then that method of sampling would bias the
result.
He suggests that a random sample would be most valid.
So how do you choose a sample that is random?
Here you might exercise
your imagination, initiative and creativity.
How much a proportion
of the population should the sample be so that it is valid?
If you interview only ten people
out of a population of several thousand, perhaps the results would not
be as valid as it might be if you interviewed a sample of one
thousand.
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