The Open Door Web Site
Going Further with Graphs Index
ICT in Biology Index
ICT IN BIOLOGY
Using MS Excel 2013 : Going Further with Graphs
Adding Error Bars
Error bars are way of showing the degree of uncertainty in a set of data. MS Excel can add them to your graphs.
Error Bars Showing Precision
The data below show the results from an experiment where the seeds from three species of plants were germinated for one week. At the end of the week the numbers of seeds germinating were counted. 25 seeds were used in each trial.
First the data is entered onto a spread sheet. The spread sheet is used to calculate the mean and the mean percentage germination. Then a bar chart is drawn using the graphing menu.
To enter the error bars first left click on one of the columns. This activates all the columns. Then, from the Chart Elements menu move to Error Bars and select More Options.
As this is a bar chart it will only offer to draw error bars on the y-axis. Select precision and enter 4. The data is calculated from samples of 25 seeds so the degree of precision is ± 1 seed. This means each seed represents 1/25 or 4% uncertainty.
Note: You will notice that you also have the possibility to enter percentage error, it should not be used this time as it will calculate 4% of each data point so the error bars will be proportional to the data (try it and you will see).
The Open Door Web Site is non-profit making. Your donations help towards the cost of maintaining this free service on-line.
Donate to the Open Door Web Site using PayPal