Dear Linda: I'm tired tonight so I'll have to recheck my own post. I think I said you can NOT subtract to get the odds ratio. What Karleen and I did is exactly the same calculation you did. But even that is slightly off the true formula -- though probably not by much. Best, Susan *********************************************** Archives: http://community.lsoft.com/archives/LACTNET.html Mail all commands to [log in to unmask] To temporarily stop your subscription: set lactnet nomail To start it again: set lactnet mail (or [log in to unmask]) To unsubscribe: unsubscribe lactnet or ([log in to unmask]) To reach list owners: [log in to unmask]