I have 3 to 5 measures of a trait per individual in two different conditions (A and B).
I'm plotting the average for each individual in each condition and I use the standard error (i.e., $SD/\sqrt{N}$, with $N$ = number of measurements) as error bars.
Now I want to plot the difference between the average measure per individual in condition A and condition B. I know I can determine the propagated error doing:
$$SD=\sqrt{SD_A^2+SD_B^2}$$ but how can I propagate standard errors (since I'm dealing with averages of measurements) instead of standard deviations? Does this make sense at all?