Here is how you can visually see the variances from the average of a range of data using the Error Bars option for charts in Excel:
You can download the file here to follow along. If you see a preview, just look for the download arrow in the upper right hand corner.
Here we have a list of students and their test scores for four different classes. I’ve added the average for each course along with the Standard Deviation:
Although this is not intended to be an explanation of Standard Deviation, here are a few notes about it:
Standard Deviation is a great way to see the range of a set of data around the average. This tells you how variant the data is. As you can see by the chart, the math scores had the lowest average, but the smallest Std Dev. This suggests that most of the students had similar struggles with the course content. In contrast, the Bio score average was higher, but the Std Dev was the highest of all, confirming that the scores ranged from 66 to 94.
Now, how do we graph this to see it visually? First we’ll start by charting the Average of each course:
Now, to add the Standard Deviation Error Bars, if in Excel 2013, click on the chart and select Chart Elements and go down to Error Bars (for 2010, look for Error Bars in the Analysis Group on the Layout Contextual tab). If you hover over the Standard Deviation option, you will see them appear. However, notice that they are all the same. That is because Excel has determined the Std Dev for ALL the scores, not just for the individual courses.
Instead we will choose More Options, then click Custom and Specify Value:
For both Positive and Negative Error Values, click on the range button and highlight the row of Std Dev values:
Click OK, and you will now see that the Std Dev Error Bars are properly proportional to the values, and indicate which had the widest and narrowest range of values:
Standard Deviation Error Bars can be used for a variety of data types – scores, investment performance, tracking your running stats, etc. Try different error bars and options, and let me know how you are able to use these in your daily routine.