1. Place the cursor in the cell where you wish the
standard error of the mean to appear, and click on the f_{x} symbol in
the toolbar at the top.

2. A menu will appear that says “Paste Function”. Select “Stastical” from the left hand side
of the menu, if necessary. Scroll down
on the right hand side of the menu and select “STDEV”; then click “OK”.

3. Click on the picture of the spreadsheet, and highlight
the numbers you averaged earlier, just as you did when taking the average. Hit enter, and “OK” to calculate the
standard deviation.

4. With the cursor still on the same cell, now click in
the formula bar at the top of the spreadsheet (the white box next to the “=”
sign) to put the cursor in that bar so you can edit the formula.

5. Put a “(“ in front of STDEV and a “)” at the end of
the formula. Add a “/” sign to
indicated you are dividing this standard deviation. Put 2 sets of parentheses “(())” after the division symbol. Put the cursor in the middle of the inner
set of parentheses.

6. Now click on the f_{x} symbol again. Choose “Statistical” on the left hand menu,
and then “COUNT” on the right hand menu.

7. Click on the spreadsheet picture in the pop-up box,
and then highlight the list of numbers you averaged. Hit enter and “OK” as before.

8. Move the cursor to be between the 2 sets of
parentheses, and type “SQRT”. Hit
enter. The standard error of the mean
should now show in the cell. Your
formula in the formula bar should look something like this, “**=(STDEV(A1:A2))/(SQRT(COUNT(A1:A2)))**”.

*(This formula would calculate the standard error of the mean for numbers in
cells A1 to A2.)
NOTE: We have calculated standard error
of the mean by dividing the standard deviation of the mean by the square root
of n. Given the formula that Excel uses
for calculation of standard deviation of the mean, this gives the standard
error of the mean after adjusting for a small sample size. This is usually the case in physiology
experiments. The formula would be
different with a very large sample size.
I do not know why Excel still does not include a formula for calculating
the standard error of the mean.*