Don't specify percentage change ambiguously

When describing a change in a percentage, always be clear whether you are referring to percentage change or percentage point change since there is usually a large difference between these two interpretations.

For example, if the conversion rate of your marketing funnel was 20% last month and 21% this month, then the conversion rate has increased one percentage point (sometimes abbreviated as +1pp). Another way to say this is that the rate has increased by 5%. However, if you tell someone “the conversion rate is up five percent” then they may assume you mean that the rate has increased by five percentage points (whether they know the baseline or not).

While that is arguably the ‘wrong’ interpretation, people erroneously use ‘percent’ to mean ‘percentage points’ sufficiently often to excuse the confusion. As always, capability for avoiding this known confusion lies with the communicator. This is the percentage change communication style guide:

Don’t describe a percentage change only in terms of ‘percent’:

The conversion rate is up five percent

This is ambiguous in a way that “…is up five percentage points” is not.

Do include the baseline and the new value when describing a change in terms of ‘percent’:

The conversion rate rose 20% from 10% to 12%

This prevents incorrect interpretation of the percent change as a percentage point change.

Prefer including parenthetical percentage point changes when summarizing:

Conversion rate: +20% (+2pp)

Consider including percent changes for context when leading with percentage points:

The error rate fell forty percentage points, a decrease of fifty-five percent

Clear metric communication is the grammar of data-driven decision making. Follow these guidelines to ensure you are understood and to give your readers and listeners the confidence that they have understood you.