Perhaps you don't understand the difference between a study and a review article?
Originally Posted by Ceist
And even more from the article... the portion you cut out preceeding the above statement:
More from the article:
"Studies of primary caretaker married fathers; egalitarian coparenting heterosexual couples; single mother or fathers after a death divorce or desertion; heterosexual single mothers by accident or choice; lesbian mothers and gay fathers after heterosexual divorce; planned lesbian motherhood through donor insemination (DI) or adoption; planned gay fatherhood through surrogacy or coparenting with women"
It's also not difficult to find research on adoptive parents, foster parents, kinship carers, grandparents, extended families etc
So basically your statement is just nonsense.
"There is no clearly identiﬁed body of research, however, to which we can easily turn. An unusually diffuse array of literatures bears indirectly on these questions..."
Maybe you can succeed where they failed and uncover an actual research study that tested the assertion that "compared to all other family forms, families headed by married, biological parents are best for children."
More likely, you'll continue to post glorified lit reviews of research that sort of addresses a point that you'd like to be true.