Here's what i've come up with:
Many studies have been carried out on the relationship of water and THC content and all seem to agree that when faced with low water supply and low humidity THC levels are increased.
These [studies] showed that under conditions of high UV-B (280-315 nm) exposure, cannabis produces significantly greater quantities of THC.
I have also come across many tips about wounding your plant to increase THC. "Wounding" refers to maybe bending the stem a little or cutting it with a clean razor. I'm told anything above these wounds, will become stronger when it heals. "What doesnt kill you makes you stronger."
I dont know the exact numbers, but I know that those who do this, definitely see in increase in crytallized resin, stem and flower growth.
Any other tips are greatly appreciated. Anyone who finds anything contrary, PLEASE post and correct the mistakes.