@inbook{2642353, author={Brenda Waning and Michael Montagne}, title={Appendix III: Critical Values of X2 Required to Reject the Null Hypothesis}, booktitle={Pharmacoepidemiology: Principles and Practice}, publisher={The McGraw-Hill Companies}, address={New York, NY}, year={2001}, url={accesspharmacy.mhmedical.com/content.aspx?aid=2642353} }