2.1: Anthropometric Indicators Measurement Guide - Linkages Project

REFERENCES PART 9.
Selecting
a Sample
3.
APPENDIX
Sampling is the process that is used to
select a representative group of individuals
whose characteristics can be described and
used to represent the whole population.
The following section outlines a few of the
problems that can result from incorrect
sampling.
Sampling Error
A lot of thought should go into how to
select the sample, and the following
examples illustrate this.
Example: You are interested in doing a
survey that will gather information on the
prevalence of underweight children
between 6 and 35 months and on the
characteristics of their households. Each
village that you will be conducting surveys
in has a clinic where mothers and their
children can be found on certain days of
the week. The clinics already have scales,
which would make them convenient. You
decide to go to the clinics and measure all
the children found there. Is this a good
sampling plan for conducting your survey
The answer is no. Mothers who go to
the clinic are considered self-selecting.
The mothers who decide to go to the clinic
might have reasons for going that would
make them different from mothers who do
not go to the clinic. They might be more
concerned with their child’s health. Or
they might be mothers who have sicker
children. Or they might be mothers who
do not have to work everyday and
therefore have the time to take their
children to the clinic.
Any characteristic that makes an
individual do something may also make
them different from the population as a
whole and have an effect on their
children’s nutritional status. When you
have a sample that is made up of people
who are not representative of the
population for a certain reason, you have
what is called sampling bias. This type of
sampling error can happen when you
select a sample from a group who all go to
a specific place, but it can also happen if
the sample is from one area of a village or
a city or among people who are neighbors.
These individuals may share some
characteristic that makes them more
similar to each other than to the larger
population.
Here are some tips for avoiding this type of
sampling error:
• Do not choose samples exclusively
from particular groups, such as children
coming to clinics.
• Do not ask mothers to bring their
children to a central point in the
community, because some of them will
not come; you will not be able to find out
how many failed to appear and how
different they may be from those who
came.
• Do not use samples chosen at will by
the interviewer, field supervisor or field
director.
9.
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