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

Entering error bars on a scatter plot

The same method can be used to put error bars on data with trend lines. This time however the menu gives you the option of x as well as y error bars.

In this example students were investigating the water potential of pieces of sweet potato tissue cut to a precise length (5 cm) and soaked in a range of sucrose solutions for 24 hours.

First the data is entered into the spread sheet. The spread sheet is then used to calculate the change in length of the tissue samples by setting up a second table.

By entering the equation =B4-5 the cell will calculate the difference between the initial length (5cm) and the final length. Press Enter for the result. The same calculation can be repeated down the column by holding down the left mouse button and pulling down on the bottom right hand corner of the cell.

Then repeated for all the data by pulling this highlighted area across the table in the same way

Finally the mean change in length and the standard deviation of the samples can be calculated too. Note it is not necessary to calculate the percentage change in length as the tissues were all the same lengths to start with.

A scatter plot graph is drawn of the mean change in length against sucrose concentration and a trend line is added.

Click left on one of the data points to activate them.

• Error Bars on a Scatter Plot continued on the next page
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© Paul Billiet 2010