z is the number of standard deviations the result mean is removed from the expected mean. For two-sided tests there's a small table at http://www.bmj.com/colle

z is the number of standard deviations the result mean is removed from the expected mean. For two-sided tests there's a small table at http://www.bmj.com/collections/statsbk/apptaba.dtl http://www.bmj.com/collections/statsbk/apptaba.dtl I submitted that booklet - which is a really good intro to statistics - at http://news.ycombinator.com/item?id=845275 http://news.ycombinator.com/item?id=845275