Thanks for your replies.
dnzrx1, it had occurred to me that these numbers could be percentages. However, as in most cases the description gives just a bare number ('+10'), but in some cases it does give an explicit percentage (I've also seen descriptions like '+5% social engineering'), I thought these bare numbers might refer to something different. Obviously not, and hence I'll just have to interpret it as the descriptions being a tiny bit negligent in this respect.
MarvinKosh, thanks for your answer. I wasn't interested in influence/defense per se, though, I just cited these as examples. I could also have mentioned for example social engineering, or research.