Error Margins added?

#1
Dear all,

this is my first post on this forum with a quick and probably very stupid question. Let's say I have value of a control distribution plus minus standard error of the mean, lets say: 2 % ± 0.5%, and a treatment, let's say 10% ± 5%). If I write there is an 8 % percent increase in the value, I would have to add both error margins as well, right? I.e. There is an increase over control by 8% ± 5.2 %. Is this correct?

Thanks a lot,
PlusOrMinus
 

vinux

Dark Knight
#2
It is depending on the situation. If you assume standard deviation is independent of the mean( this is normally assumed in many cases) , the increase in mean only influence the mean value