Dr. Garfinkel mentioned the outcomes of the Fragile Families research “provide no support for the culture of poverty thesis,” which posits that totally different values and behaviors among the many poor lure them in self-perpetuating cycles of privation. Rather, he mentioned, “circumstances and opportunities,” not worth variations, have the best impression.

Though her findings rankled some advocates for single moms, Dr. McLanahan continued to publish books and papers on the subject.

“We reject the argument that people should not talk about the negative consequences of single motherhood for fear of stigmatizing single mothers and their children,” Dr. McLanahan and the researcher Gary Sandefur wrote of their 1994 e-book, “Growing Up With a Single Parent: What Hurts, What Helps.” “While we appreciate the compassion that lies behind this position, we disagree with the bottom line. Indeed, we believe that not talking about these problems does more harm than good.”

Sara Frances Smith was born on Dec. 27, 1940, in Tyler, Texas. Her father, Norman Smith, was a common supervisor for an area oil firm. Her mom, Iredell (Brown) Smith, was a homemaker.

She attended Robert E. Lee High School in Tyler, now often called Tyler Legacy High School. A gifted pianist, she studied at the Aspen Music Festival in Colorado for a summer season. She attended Bennett Junior College in Irvington, N.Y., and went on to Smith College. After a 12 months at Smith, she dropped out in 1962 and married Ellery McLanahan. They had three youngsters, Sara, Ellery and Anna Bell, all of whom survive her. The household moved to Houston, and the couple divorced in 1972.

Dr. McLanahan returned to high school and graduated from the University of Houston with a bachelor’s diploma in sociology in 1974. She acquired her masters and doctoral levels in sociology from the University of Texas at Austin.

She started her postdoctoral fellowship at the University of Wisconsin in 1979. It was there that she met Dr. Garfinkel and targeted her analysis on single motherhood. (She had prevented the subject in her doctoral thesis at the University of Texas as a result of, she mentioned, it felt too near dwelling.) She and Dr. Garfinkel married in 1982.