MisterLock

It has always been 25 % for scratches and 96 % for bites.
And when I mean always, I mean it, back way in the 1.5D day's(most of you weren't around during that version).
Also I thought thick skinned and thin skinned affected what is the chance to receive an injury from a zombie when it does a full lean on animation, not that it affected the chance of infection also...

This topic has already been discussed numerous times,and it is in the works,the devs said it themselfs,there is even a video about it from them but not sure where,they also want to implement you having a chance of catching the zombie infection if you leave bodies somewhere to long.