Marriage Law Project Publications

No Basis: What the Studies Don’t Tell Us
About Same-Sex Parenting

— Robert Lerner, Ph.D., and Althea K. Nagai, Ph.D.

Full Text (PDF - 479 KB)

Executive Summary

It is routinely asserted in courts, journals and the media that it makes "no difference" whether a child has a mother and a father, two fathers, or two mothers. Reference is often made to social-scientific studies that are claimed to have "demonstrated" this. An objective analysis, however, demonstrates that there is no basis for this assertion.

The studies on which such claims are based are all gravely deficient.

Robert Lerner, Ph.D., and Althea Nagai, Ph.D., professionals in the field of quantitative analysis, evaluated 49 empirical studies on same-sex (or homosexual) parenting.

The evaluation looks at how each study carries out six key research tasks: (1) formulating a hypothesis and research design; (2) controlling for unrelated effects; (3) measuring concepts (bias, reliability and validity); (4) sampling; (5) statistical testing; and (6) addressing the problem of false negatives (statistical power).

Each chapter of the evaluation describes and evaluates how the studies utilized one of these research steps. Along the way, Lerner and Nagai also offer pointers for how future studies can be more competently done.

Some major problems uncovered in the studies include the following:

Unclear hypotheses and research designs

Missing or inadequate comparison groups

Self-constructed, unreliable and invalid measurements

Non-random samples, including participants who recruit other participants

Samples too small to yield meaningful results

Missing or inadequate statistical analysis

Lerner and Nagai found at least one fatal research flaw in all forty-nine studies. As a result, they conclude that no generalizations can reliably be made based on any of these studies. For these reasons the studies are no basis for good science or good public policy.

Four Appendices follow. Appendix 1 is a bibliography of the studies and related publications. Appendix 2 is a table that summarizes the evaluation of each of the studies with regard to each research step. Appendix 3 (by William C. Duncan) is an overview of how these studies have been used in the law. Appendix 4 (by Kristina Mirus) describes how the media has covered these studies.