Yates' correction for continuity, or Yates' chi-square test, adjusts the formula for Pearson's chi-square test by subtracting 0.5 from each observed value in a 2 X 2 contingency table. This formula is chiefly used when at least one cell of the table has an expected frequency less than 5.
Other sources say that this correction should be used when the expected frequency is less than 10.
