# Finite Population Correction

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The finite population correction is used when the sample size is a large fraction (approximately 5% or more) of the total population. You can apply a finite population correction in Q as a design effect on a table.

The formula for the finite population correction is ${\displaystyle {\sqrt {\frac {N-n}{N-1}}}}$, where ${\displaystyle N}$ is the total population and ${\displaystyle n}$ is the sample size. However, when calculating this correction for use as a design effect in Q, you should not use the square root.

To apply this correction to a table you should:

1. Calculate the correction outside of Q. Remember to use ${\displaystyle {\frac {N-n}{N-1}}}$ (i.e., without the square root).
2. Select the table and go to Edit > Table Options > Statistical Assumptions.
• Set Proportions to z-test and uncheck Bessel's correction.
• Set Weights and significance to Un-weighted sample size in tests.
• Put the finite population correction that you calculated previously in the Extra deff field.

Note that this procedure applies to the whole table, so if you have a table with multiple sub-populations, you should filter the table to only show the sub-population of interest.