I was studying Biostatistics by Zar, the Yates' correction part and stumbled upon this: My doubts: The conculsions are not taking place exactly at the level of alpha- what does this mean? Do the values of Chi square mentioned in table not correspond to the alpha(probability) indicated? Is the corresponding value actually a range? I also don't understand what it means by 'This situation would be unfortunate were it not for the fact that the approximation is a very good one, except when df=1. In the case of df=1, it is usually recommended to use Yates correction for continuity.' Why is Yates' correction specifically done when df=1?