Graph tip - How to make some error bars to go up, and some to go down.

This example shows how to make some error bars go up and some go down.

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Change direction of all error bars in a data set

You can show only the half of a bar that is above, or below, the mean value. This is particularly useful on an XY graph, to prevent error bars from adjacent data sets from running into one another.

To format all the points of a data set to display just the top or bottom halves of all error bars, click on one of the symbols for that data set to open the "Format graph" dialog. In the "Error bars" section, make the appropriate choice from the "Dir." drop-down box. This applies to bar graphs as well.

Change direction of error bars for each symbol individually

If you want half error bars for some, but not all, points in a data set, right-click on the data point you want to format and choose Format This Point/Error Bar direction. This only works with Prism 5 or later.

Note a bug in Prism 7.00 and 7.01 Windows. If you choose to plot connecting line and error bars, but no symbols, the Error Bar Direction menu choice will be gray and so is not avallable. Easy workaround. Turn on plotting of symbols first. Then right click and choose the error bar direction for each point. Then turn off the plotting of symbols. 

Entering separate up and down error values on the data table 

On the Welcome (or New Table dialog), you can choose the Mean, +Error, -Error setting so you can enter different error values for the upper and lower error bar. You can leave one of these values blank to show an error bar in one direction only. 

Prism then leaves room for differing positive and negative error limits. Enter zeros (or just leave the cell blank) on the table wherever you don't want that half of the error bar to be displayed. This method will work with both Prism 4 and Prism 5 or later.

Download this file to see how this graph was made.