Sample Size Calculator
What does a sample size calculator do? When you know
how accurate you want your data to be, and you know the size
of your target population, then you need to calculate how
big a sample you need to draw from that population in order
to have survey results that can be projected onto the target
population. See below for a basic explanation of the
relevant statistic procedures, and see the box at right to
choose a sample size calculator. |
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About the Sample Size Calculator
Sometimes you know how accurate you want your data to be, i.e., you have a
desired margin of error (see Basic
Statistical Testing for how to calculate the margin of error), and you
know the size of the population you want to get information on. Then you need
to know how many people in that population you need to actually talk to in order
to have results that can be projected onto the entire population with the desired
amount of accuracy.
To calculate the desired sample
size when your results are going to be in proportions or percentages,
youll need to know your desired confidence
level, desired margin
of error, and, if known, the estimated proportion or percentage you
expect to find. If you dont know, then you can guess 50 percent, since
a 50-50 split is the worse case scenario.
To calculate the desired sample size when your results are in means or averages,
you dont need to give an estimated result, but you will need to estimate
a standard
deviation for your data set.
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