Our very own DextroWombat proves his inventiveness by discovering the formulas for calculating potion effect strength and duration.
I asked the question about the formulas on the UESP forums and DextroWombat bravely accepted the challenge of brewing an ungodly amount of potions, dilligently recording all the variables and outcomes and finally coming up with the best-fit formulas for the recorded data points. His final formulas can be found in the Morrowind Alchemy article on the UESP.
Potion maker update
This discovery means that the potion maker now displays the expected strength and duration for each effect, active or inactive. Of course, for this to work, you first have to select the tools your character will be using and the values for his or her intelligence, luck and alchemy skill level.
Some effects might not work as intended just yet (Dispel, for example), and that will be fixed in the future. I will also add the potion weight and monetary value calculations when those are determined. I'm also planning on adding a more convenient way to select ingredients.
As always, I will be very grateful for any bug reports or suggestions. You can send those using the contact form.