How to express the difference between two percentages? If I have some share of a product in some sector as:
2012 2013
50%  60%

and I find share change for 2012-13 then should it be 10% or 0.1?
 A: In particular
Do not use 0.1. The absolute shares are not expressed this way and the unit is missing, which can be misleading.
In general
As an alternative to relative / absolute difference (suggested by charles), one can use the term percentage points to express absolute difference while still use percent for relative difference.
In your example the share increased by 10 percentage points and increased by 60/50-1=20 percent.
But I have to admit, I first heard the term percentage points in this xkcd, so the terms relative and absolute difference might be more commonplace and hence easier to understand:

A: I don't think there is a true conceptual difference between 0.1 and 10%. School teachers will perseverate on the difference, but I think the rest of us can relax. 
What you want to make sure you're expressing is that you are using an absolute rather than relative difference (or use the corresponding terminology that exists in your field). 10% here is an absolute difference in product share. 
