After looking for a solution for good 2 hours, I decide just to ask for help in a nice forum.

I have a field experiment with 4 different plots. In each plot I collected and analysed 3 samples and calculated the mean and SE of each plot.

Plot 1: M1=0.2 (SE1=0.02)

Plot 2: M2, SE2

Plot 3: M3, SE3

Plot 4: M4, SE4

Anyway, now I wanted to calculate the average for the 4 plots M and its SE.

My idea is to calculate the sum of SE's, divide this by 4 and do the squareroot of it:

SE=SQRT(( (SE1^2)+(SE2^2)+(SE3^2)+(SE4^2)) /4)

Is this the right way to do it?

Or are you dividing by 4 after doing the squareroot of the sum?

SE=(SQRT((SE1^2)+(SE2^2)+(SE3^2)+(SE4^2))) /4

Or is this way completely wrong?

Thank you so much in advance!

SoilScientist