Mathematicians say they’ve confirmed an age-old rule of fashion: that trendy women’s styles get recycled every 20 years or so. For the study out of Northwestern University, researchers pulled together a database of some 37,000 garments spanning nearly 160 years, combining archival sewing patterns with runway images dating to 1869, reports Popular Science. They converted design details like hemlines, waist placement, and necklines into numbers, then built a model to track how trends shift between novelty and familiarity. And voila: They found that patterns and themes reemerge roughly every two decades.
“We have all experienced the idea that fashion comes back—that miniskirts are back, or bell-bottom jeans are back,” lead author Emma Zajdela tells BBC Science Focus. “As mathematicians, we were curious to prove or disprove this theory—and recent advances in computer tools and digitized records have made this possible.” The data show clear oscillations, most visibly in skirt lengths, which have swung from flapper-era short to midcentury long to 1960s mini and back again.
The pattern, however, may be weakening: Over the past four decades, options have multiplied (think mini, midi, and maxi dresses coexisting), and conformity has declined. “Trends in fashion have been accelerating since the mid-1980s, making the 20-year rule less apparent—although still very present—in the data,” says Zajdela. “Instead, there has been an increase in the variety of styles available.”