When the sample size is small, we should disminsh the difference between the observed and expected values, in each cell of the table.

This is obtained by a modification in the previous formulae: X2 =(|ad – bc|) – N/2)2 x N /(a+b) (c+d) (a+c) (b+d)

Vertical bars to the sides |ad-bc |, show that we need take the absolute values from ad-bc. So, if this value is negative, we do not take into account the sign and take the positive value.

N/2 is called the continuous correction.

The results between the formulae with and without continuous correction are slightly different, because to the continuous correction.