Children's books are biased towards stories that feature male lead characters, even when the characters are animals, according to the largest study of 20th century children's books undertaken in the United States.

Children's books are a "dominant blueprint of shared cultural values, meanings, and expectations," the authors of the study noted. The under-representation of female characters sends the message that "women and girls occupy a less important role in society than men or boys."

The study appeared in the April issue of Gender & Society, a highly-ranked peer-reviewed journal published by Sociologists for Women in Society. It examined nearly 6,000 books published from 1900 to 2000.

"We looked at a full century of books," said Prof. Janice McCabe, Assistant Professor of Sociology at Florida State University and lead author of the study. "One thing that surprised us is that females' representations did not consistently improve from 1900 to 2000; in the mid part of the century it was actually more unequal. Books became more male-dominated."

The study found that 57 percent of children's books published per year contained males as central characters. Only 31 percent featured female lead characters.

In children's books that included animal characters, 23 percent of the central characters were male, while only 7.5 percent were female. Adding to the biased towards male lead characters, the authors of the study explained that readers tend to interpret gender-neutral animal characters as male.

"Together with research on reader interpretations, our findings regarding imbalanced representations among animal characters suggest that these characters could be particularly powerful, and potentially overlooked, conduits for gendered messages," the authors of the study said. "The persistent pattern of disparity among animal characters may reveal a subtle kind of symbolic annihilation of women disguised through animal imagery."