What percentage of infertility cases are due to a cause involving only the male partner?

The answer to this question is 20 percent.

In general, women has more roles during the fertility process, so their margin of error will be significantly higher compared to the male counterparts.

The male's role during fertility process is to insert the sperm, while the women have to face potential mistakes in their uterus, their nutrition, their eggs condition, their hormones, external accidents, etca