Percentage change, difference and the spreadsheet formula that produces it, including the case everyone gets wrong.
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Percentage change = (new - old) / absolute value of old, formatted as a percentage. The ABS matters: without it, a change from -50 to -25 reports as -50 percent when the value actually improved.
Percentage change is undefined, not infinite and not 100 percent. Any tool that prints a number there is making one up. Report the absolute difference instead, or restate the baseline.
So negative baselines behave. Going from -50 to -25 is an improvement, but dividing by -50 gives -50 percent, which reads as a decline. Dividing by the absolute value gives +50 percent.
Different things, and mixing them misleads. Moving from 20 percent to 25 percent is a rise of 5 percentage POINTS, and also a 25 percent increase. Say which one you mean.
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