I am getting a number below zero when caluclating out two standard deviations from the mean. Is this ok? I am not a math wizard, so please keep your response simple enough. I need to complete a statistics screening exam for a methods course later on today and I am hung up on one topic that came up during the practice test. The data set I got was in reference to the number of homicides that have occurred in a number of cities. This range of the data is 0-5. When I am putting together confidence intervals and calculating out as much as two standard deviations from the mean I am getting low values that are negative. Obviously you can not have a negative number of homicides. When calculating the confidence intervals and out to two standard deviations from the mean should present the low value at ZERO or should I actually present the negative number? For example, if a 95% CI caused the calculation to be -1.5 to 3, would I present that or would I present 0 to 3? Thanks.

This is certainly fine. What you tell me, 95% of the data is between -1.5 and 3. That is a correct statement. But it is even better, 95% of the data is between 0 and 3 for the precise reason that you indicate.
