Fashion is no frivolous topic for Professor of Sociology Diana Crane, Ph.D.

In fact, she considers the study of human duds to be an excellent way of documenting such large issues as changing gender roles, the emergence of feminism, and the fragmentation of social classes over the past century.

Consider, for example, hats and T-shirts.

“Between about 1850 and 1960, men weren’t fully dressed without hats,” Crane said recently. A man’s hat defined his occupation and his social position, from the English lord to the Paris rag-picker, she said.

That changed in the socially turbulent 1960s. The hat disappeared — supplanted in its rigid role of class definition by the ubiquitous, slogan-bearing, individualistic T-shirt.

Now about a billion T-shirts are sold each year in Europe and North America, shirts “worn by both rich and poor to express a wide variety of social affiliations, beliefs, organizational affiliations,” Crane said.

A specialist in art, the media, high culture and popular culture, Crane has researched fashion using both historical documents and focus groups. Her book “Fashion and its Social Agendas: Class, Gender and Identity in Clothing” is scheduled for publication by the University of Chicago Press this month.

Studying fashion was a natural choice for her, “partly because I’ve been immersed in culture for a long time, but also because I spend a lot of time in Paris,” Crane said. “My husband [Michele Hervé, a former economist for UNESCO] lives there, and I spend several months a year there. ...Fashion is all around you.”

Even in the heyday of haute couture, with its yards of petticoats and inconvenient ruffles, Crane believes that more women than a few mere eccentrics were disposed to go their own way — albeit privately.

In researching the early efforts by feminists such as Amelia Bloomer to design clothing for women that matched the convenience of men’s clothing, Crane discovered photograph upon photograph of women wearing ties, shirtwaists and bloomers, indicating that such pseudo-male styles were more popular with women than fashion historians have acknowledged.

And with the fragmentation of society, that independence has continued to grow.

“You begin to get fashions that were created by people in working-class youth cultures,” Crane said. “You get a lot of different lifestyles, so that people in the upper class are not all the same, and people in the middle class are not all the same.”

While the glamour of a fashion center such as Paris remains, its power is diminished by so many choices: “[Today’s] upper-class woman may feel she has to dress in a trendy fashion but — unlike 100 years ago — what she wears has little influence on society as a whole,” Crane said.