# How to express an increase in percentage unambiguously?

So I have a metric, say, accuracy, which is originally 70% and then raised to 80%. I want to say the accuracy increases by 10%. But it is ambiguous, as some may interpret it as the current accuracy is 70%·110%. How can I say it so that people will undoubtedly understand the increased result as 70% + 10%?

This is a very relevant question to ask.So often it is unclear what people mean.

For my own part I only say "it has increased by 10%", if I mean exactly that i.e, in your example, from 70% to 77%.

Otherwise I would say "it has risen by ten percentage points" - meaning from 70% to 80%.

• Very good, "ten percentage points" is just right. However many retail promotions seem to use the confusion deliberately by wording adverts such as "Our 50% sale items now have another 10% off" actually meaning that the items are now on sale at 45% of their pre sale price but leading people to think that they on sale at 40% of that price. – BoldBen Feb 12 at 10:36
• @BoldBen Another instance of confusion is over opinion-poll voting shares. Sometimes you will hear commentators say "The Conservatives share of the vote has increased by 4%". (i.e. from 37% to 41%). The better quality newspapers will say "has increased by four percentage points" as does The Times in a front-page article today. – WS2 Feb 12 at 17:57
• I'll agree with that, it seems that advertising copy and newspaper copy suffer from the same type of mathematical imprescision. – BoldBen Feb 12 at 21:08

The original accuracy was increased/has increased/increased from 70% to 80%.

• It doesn't work when I want to say three metrics all rise by 10%. – Siyuan Ren Feb 12 at 13:08
• Sorry, I don't see what the problem is. You have just said "all three metrics rise by 10%", which seems perfectly clear... – user218195 Feb 13 at 11:26
• It is clear in this context. In other context, people may interpret it as all metrics rise to 1.1 times their original value. – Siyuan Ren Feb 13 at 13:38