Damage effectiveness and critical strike

Hi!
I´ve een pondering my next build and have a question. Does a reduced damage effectiveness also affect critical damage?

Say that I have a skill listed as doing 100 fire damage.
Say that I do 150% crit damage.
Now I do 150 fire damage.

Does damage effectiveness reduce this number?

Now assume that I use a gem with 20% damage effectiveness.
Does that reduce the skill damage to 20 even though its listed as 100 on the same skill?

If not, does it reduce the crit damage multiplier by 80% = (30% crit dmg)?

Noone?

I don't really understand it well enough to explain it, but yes, dmg effectiveness would reduce dmg after a crit. If you've a gem with 20% dmg eff, I think you'd work out the total dmg of the hit, in your case 150 fire, then apply ~ so 30.

Yes it does

They are separate multipliers.