I know that there are formulas for switching from and to sourdough and or preferments, but even though my library grows I haven't found such a formula. I have a general idea of the fact that a sourdough bread usually requires around 40% of sourdough and a regular yeasted bread requires something from .1% to a stunning value of 2% of yeast. Other that this general idea I have not found anything in the literature I have at home since most of the books usually treat these subjects separately.
Is there a formula that transforms a recipe from fresh yeast to sourdough and vice versa? What about preferments?
EDIT: The question is under the assumption that a started is intended as a 100% hytration one, if you know of a conversion for a 50% hydration starter or pasta madre feel free to pitch in.