Overview
This lecture covered how to represent data variation using averages and standard deviation in Excel, and how to display this information using error bars for more informative graphs.
Averaging Data in Excel
- Combine multiple data sets by calculating the average (mean) for each category.
- To calculate the mean, add all data points together and divide by the number of data points.
- In Excel, use
=AVERAGE(range) to quickly compute averages over multiple cells.
Standard Deviation and Data Variation
- The mean alone can be misleading if variation is not shown.
- Standard deviation measures how spread out data points are from the mean.
- In Excel, use
=STDEV.P(range) to calculate the standard deviation for population data.
- Standard deviation helps reveal differences between data sets with similar averages.
Adding Error Bars in Excel
- Error bars visually represent standard deviation or variability in graphs.
- In Excel, select the chart, click the green plus (+) sign, and choose "Error Bars."
- Use the "More Options" and "Custom" settings to specify calculated standard deviation values for error bars.
- Set both positive and negative error values to reflect your data’s standard deviation.
- Google Sheets may have limited functionality for custom error bars compared to Excel.
Interpreting Graphs with Variation
- Two data sets can have identical means but very different variability.
- Error bars help identify if results are consistent or variable across data points.
- Displaying standard deviation in your graphs provides a more honest representation of your data.
Key Terms & Definitions
- Mean (Average) — Sum of all data points divided by the number of points.
- Standard Deviation — A measure showing how much values differ from the mean.
- Error Bars — Graphical representations of data variability, usually using standard deviation.
Action Items / Next Steps
- Practice adding averages and standard deviations to your data in Excel.
- Add custom error bars to your chart using your calculated standard deviations.
- Review assigned articles and YouTube tutorials on error bars and Excel chart options.
- Ensure your final project poster includes graphs with standard deviation/error bars.