What makes a fair comparison?
A comparison needs a common question before it needs a common chart.
The short answer
The base is the reference observation used in your calculation. Choose it because it matches your question, rather than because it produces the most striking result. Keep the start and end dates aligned, and check that both measures use compatible definitions.
A worked example
Suppose A starts at 50 and finishes at 60, while B starts at 200 and finishes at 220. B adds 20 units; A adds 10. But A grows by 20%, while B grows by 10%. Choosing the largest increase in units answers a different question from choosing the largest relative increase.
Your turn
Try writing two headings for the same data: “Change in pounds” and “Change from the starting value”. Calculate each before deciding which belongs in your note.
What this does not tell you
An illustrative calculation does not explain causes or predict future results. Check the dates, units and missing observations before using the method elsewhere.
Related term
Base valueSources & review
Original Charts Haven example. All stated numbers are illustrative and allow you to repeat the calculation.
Next lesson: Ask a better question