MS-EXCEL: GOING FURTHER WITH GRAPHS I: ADDING ERROR BARS

Error Bars Showing Standard Deviations

If you want to show standard deviations as error bars then you need to use a slightly different approach.

These data come from an investigation on the growth of moulds sampled from different parts of two cheeses (Camembert and Rocquefort) and grown on malt agar in a Petri dish. The growth of the mould was measured after one week.

The data is entered on a spread sheet. The spread sheet is used to calculate the mean and the standard deviations. A bar chart is drawn of the results.

Click left on one of the bars, then double click to get the data format menu.

Select error bars both above and below the data point and then select Custom (Fr: Personnalisée)

Now the data that is to be used for the error bars has to be selected. Click left on the upper bar (+) the menu will disappear and you will be left with the box in which you have to select the cells containing the data for the error bars (in this case the standard deviation).

Left click on the first cell and hold the button down whilst you run along the line for standard deviations. You will see the cell coordinates appear in the box.

Let go of the mouse button and the menu will reappear with the upper error bar box complete.

Repeat the procedure with the box for the lower error bar (-). Use the same cells for the standard deviations as before.

Press Enter or click OK and the error bars will appear on the graph.

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© Paul Billiet 2010