The researchers found that 20.94% of the adult population in Michigan identify as childfree, meaning they do not have and do not want biological, step, or adopted children.

I skimmed the study and it looks like they did not differentiate between types of children (i.e. biological or not). One example question from the study: “Do you plan to have any biological or adopted children in the future?”

While not the point of the study, I wonder if there is a significant population that is interested only in adopted (or maybe step-)children. Especially given the recently reported rise in couples forgoing procreation for climate and/or "why would I bring a child into this shitty world" reasons, it would be interesting to learn if this population would be interested in raising non-biological children instead (the idea being they are not increasing the number of children in the world, but rather helping to care for the ones already here). Similarly not included in this study: people only interested in fostering children but not adopting (this can get murky however as sometimes fostering does lead to adoption, but usually not).