sgupta0827

Yes, I remember seeing them both in the text at different locations. (i.e. 3 and 2.58)

I guess both are correct, 3 being more conservative than 2.58. So, if there is a choice between 3 and 2.58, I would choose 3. i.e. if a value lies between +- 2.58 standard deviations, it must for sure lie between +-3 standard deviations too.

Someone, please comment on this.