Hi - I have a quick question. I understand that the sum of two normal distributions is a normal distribution. Now let's say I have the z-score from one normal distribution and the z-score of another set of data that is also normally distributed and a third and a fourth etc. I just want to know if it is mathematically allowed to ADD the z-scores together? I do not care too much about the probability (p-value). I would like to know if it is allowed and are there any internet references on this topic? Thank you very much.