The relative risk computed by InStat is incorrect.

We discovered that InStat (up to 3.06 for Windows, and 3.0b for Mac) can give the wrong result for relative risk when some of the values are huge (in the millions). With large numbers, InStat usually gives an error message but can sometimes give an invalid answer.

This bug is not in Prism or the QuickCalc free web calculator. Fixed in InStat 3.1.