Women run just a quarter of the biggest art museums in the United States and Canada, and they earn about a third less than their male counterparts, according to a report released on Friday by the Association of Art Museum Directors, a professional organization.

The group examined salary data on the 217 members it had last year through the prism of gender, for the first time. The report noted strides made by women at small and midsize museums, with budgets under $15 million, often university or contemporary-art institutions. Here, women have basically achieved parity, holding nearly half of the directorships and earning just about the same as men. But the gap is glaring at big institutions, those with budgets over $15 million: Only 24 percent are led by women, and they make 29 percent less than their male peers.

And just five of the 33 most prominent art museums — those with budgets greater than $20 million — have women at the helm.

Image Olga Viso of the Walker Art Center. Credit... Alexander Tamargo/Getty Images for Design Miami

“There is a difference if a woman is running one of these big museums,” said Elizabeth Easton, director of the Center for Curatorial Leadership, a training program in New York that has helped place nine women in directorships, but none at the country’s most influential museums. “Those directors are the most loud and authoritative voices. It sets the tone.”