Adding Error Bars

Adding error bars is not too difficult, but does take a few more steps in Excel than it probably should. Worse still, if you make a mistake, Excel will add the wrong error bars. Make sure to check that the values on the graph match those that you calculated when you have completed all of the steps. Speaking of checking up, when was the last time you saved your workbook?

The first step is to click on the plus sign in the upper right-hand corner of your graph, to bring up the "Chart Elements" menu:

Click on the box next to "Error Bars", as indicated by the red arrow above, to add the wrong error bars. That's right, I said "wrong error bars". Well, technically I typed it...

Not to worry! We're not done. See that grey arrow that appeared next to "Error Bars" when you checked the box?

Click on that (as indicated by the red arrow above) to access the dropdown menu (also shown above), and click on "More Options". This will bring up a large "Format Error Bars" menu on the right-hand side of your screen. You will have to click on the icon with the bars (red arrow below) to get to the correct menu:

At the very bottom of that menu (blue arrow on the preceding picture) click on the circle next to "Custom". This will bring up a selection box that should look somewhat familiar:

In the same way you selected the values for your graph, select the 2 standard errors from the table you made for both the positive and negative error values, as the error is the same magnitude in both directions (remember, this is just a visual depiction of "mean∓SE"). You will have to click on the tab at the bottom to go to the worksheet where your data are. Click "OK", and you should have the correct error bars in your graph.

Only one issue remains. As with the text and graph borders, Excel defaults to grey as a color...presumably because black is just too pleasantly visible. This is an easy fix. Click on the paint can icon at the top of the "Format Error Bars" menu, click on the circle next to "Solid line", and if that doesn't change the color to black, click on the paint can icon next to "Color", and select one of the black squares. Your graph for the fish data should look like this:

As a rule of thumb (which we no longer will need once we learn some proper analytical techniques), if the standard error bars overlap, the means do not differ. Apply this rule of thumb to answer:

Question 5: Examine the graphs for both sets of data (birds and fish), and conclude whether or not the means differ in each case.

As always, save your Word document and Excel workbook as "yourlastnameex3", and submit via Blackboard.