Participatory Impact Assessment - Capacity4Dev

STAGE FIVE:
SAMPLING
Your sample size and method will ultimately be determined by the time and resources you have
available for the assessment, and decisions and choices will have to be made depending on what
level of representation and evidence you hope to achieve.
Broadly speaking, there are three types of sampling method which can be used for a participatory
impact assessment:
1. Convenience Sampling (go to easily accessible villages)
2. Purposive Sampling (go to villages “typical” of the project area)
3. Random sampling (put all the names of the project villages in a hat and pick out the number
you plan to assess)
Although random sampling is considered to be the most scientific, and convenience sampling the
least, each method has its strengths and weaknesses. For example, convenience sampling may save
time, but all the selected villages being easily accessible may not be representative of the greater
project area (road side bias). Alternatively random sampling may give more truthful results, but it
can be costly and time consuming. With purposive sampling, there may be a tendency to go to
villages where you think your project worked well, and where the results will show an impact that is
not representative of other villages in the project area. One way of minimizing this tendency is to
deliberately select equal numbers of good, bad and medium villages.
Although, there is no right or wrong answer on sampling method, you do need to consider the end
users of the assessment findings. If you wish to influence policy, or publish the findings in an
academic journal, then it is important to use random sampling if you want the results to be accepted.
If the results are for internal use only, then random sampling is probably not necessary. Although it
is not essential to use a random sample, and it is often not practical, if you wish to extrapolate the
results to make decisions that will apply to the entire project area, you need to use a random sample.
For example, if you implement a project in 50 villages, and you plan on assessing only 10 villages,
you would have to randomly select the 10 villages. The only other option would be to asses all 50
villages. If on the other hand you decided to purposively select 10 villages, there is nothing wrong
with this but the results would only be applicable to the villages assessed and could not be
extrapolated to the other 40 project villages.
Similarly there is no correct answer on the actual sample size. For most project impact assessments,
the important thing is to capture the overall trend, and this can usually be done with a smaller sample
size. As long as it is done systematically it can be representative. Nevertheless, there are a number of
factors that need to be taken into consideration. Your sample size will depend on the type and
number of questions you are trying to answer, and the number and type of assessment tools and
attribution methods needed to answer these questions (see next section). For example, if you decide
to use control groups for attribution, you may be able to get a greater level of evidence with a
smaller sample, even though a control group immediately doubles the size of your sampling frame.
Again some tools, such as “pair-wise” and “matrix” ranking are extremely time consuming, and will
be more suitable for focus group discussions. To use these tools for household interviews would
imply reducing your sample size considerably.
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