There is a 1% chance (prior to any boost) while tradeskilling for a global drop to occur. Miden Shard drop chance is unaffected by boosts and is on a seperate roll, which is why the odds don't add up to exactly 100%
The global drops are as follows: Gems, Keys, Relics, Gold, Magic Elements, Equipment, or Resource Bags.
The chance for a global drop to be a particular item is as follows:
Upon winning in combat you have a chance to receive a permanent boost of either Health Points or Magic Points.
The chance to receive this boost is reduced if you fight monsters that are not appropriate for your level. By fighting monsters that are 50% or weaker than your level (For example a level 100 player fighting a level 50 monster) you will have a reduced chance of finding permanent stat boosts.
The exact chance when fighting monsters of appropriate level is as follows:
1.2% chance of an increase of 1 Health or Mana point
0.03% chance of an increase of 25 Health or Mana point