How much weight reduction occurs after roasting coffee beans? Does the roasting process lead to weight reduction? If so, what are determining factors? type of coffee? type of roast(dark, medium etc) ? 

If you have X lbs of unroasted coffee beans, how much (average) roasted coffee beans you get after roasting?
The roasting process leads to water loss in all types of beans. Most beans start off at about 10-12% moisture and end up around 3%.
My experience gives about 15% weight loss (shrinkage) for light roasts and around 20% on dark roast profiles.

Example of a dark roast weight loss in my roasterie would be: 
Starting weight: 240#
Roasted weight: 195#
Shrinkage = 195/240 = 81% of start weight so 19% loss.

I can't seem to find any online documentation of this. Just daily experience of being a professional roaster.