how do you combine standard errors into one


New Member
I would like to display some data in a bar graph. Each column on the x-axis is composed of two values to give a larger total. I have standard errors for the smaller individual values, but would like to report only the standard error for the combined total value.

The values in the y-axis were derived from the linear equation of a regression analysis on continuous data (friction vs. time)

Any help would be greatly appreciated.