BLOOMBERG | KATYA KAZAKINA

It used to be so simple at fashion shows. When stocks were soaring, skirts rose with them to mini length. When the markets headed down, hemlines dropped to more modest levels.

This year, it’s not so straightforward. Three days into New York’s Mercedes-Benz Fashion Week, luxury retail consultant Robert Burke was scratching his head trying to find anycorrelation between the runway’s different styles and the economy.

“Hemlines are all over the place, very much like the stock market,” Burke, president of Robert Burke Associates in New York, said in an interview.

In the past month, the Standard & Poor’s 500 Index dropped from 1121.06 on Aug. 10 to 1047.22 on Aug. 26, climbing back to 1109.55 on Sept. 10 for its biggest two-week gain since June. The 97 designers presenting Spring 2011 collections this week feature similar ups and downs -- with everything from micro-mini skirts to floor-swooping maxi pieces made with transparent organza and chiffon.

“We are living in a universe where there’s no hemline edict,”Fern Mallis, a fashion industry consultant, said in an interview. “The old adage doesn’t apply any longer.”

Mallis was referring to a maxim known as the “hemline index,” a 1920s theory attributed to the economist George Taylor that suggested a correlation between hemlines and economic growth.

This time around, BCBG Max Azria had some dresses so short that they could have passed for tunics, and others that reached the ankle, clinging to the models’ long-limbed bodies like fancy nightgowns. Meanwhile, designer Prabal Gurungdropped his hemlines below the knee and, on occasion, even below mid-calf.

Higher Hems

In the 20th century, dresses crept up for the first time around 1915, during World War I, said Daniel James Cole, a fashion historian. Around the same time, the U.S. economy expanded for 44 months, starting in December 1914, according to theNational Bureau of Economic Research.

“The hem went up to mid-calf,” said Cole, a professor at the Fashion Institute of Technology in New York. “That was radical, because the hemline of the 19th century was to the shoe.”

The prosperous “roaring twenties” saw the emergence of flappers, who provoked anger by bobbing their hair, smoking in public and wearing knee-length dresses.

The stock market’s crash of 1929 was a defining moment for the economy and skirt heights, Cole said. Both plummeted, with hemlines below mid-calf. The S&P Index dropped 86 percent from Sept. 6, 1929, through July 8, 1932, according to data compiled by Bloomberg News.

Knee-Length

A decade later, on the eve of the World War II, the U.S. economy entered an 80-month expansion which lasted through February 1945, according to the National Bureau of Economic Research. During this time, knee-length skirts became ubiquitous, though the trend “had more to do with conserving fabric for the war effort than with the economy,” Cole said.

As a reaction against wartime’s austerity and fabric rations,Christian Dior’s first fashion collection in 1947 offered luxurious silhouettes with full skirts reaching below mid-calf.

“The hemlines dropped by 10 inches,” said Cole. The S&P fell 28 percent between May 29, 1946, and May 19, 1947.

During the 1960s, the U.S. economy grew for 106 months, making it the second-longest expansion between 1857 and today, according to the National Bureau of Economic Research. Hemlines reached their highest.

Twiggy Miniskirts

By 1966, miniskirts became a must in women’s wardrobes. British designer Mary Quant and teenage model Twiggy helped popularize the style.

“In 1966, you had to wear a skirt that was at the knee or higher, or you’d look ruefully out of fashion,” Cole said.

With the S&P dropping 36 percent from Nov. 29, 1968, to May 26, 1970, hemlines moved back to modesty. On March 13, 1970, Life magazine addressed the style transition with a cover story, “The Great Hemline Hassle.” On Aug. 21, 1970, the publication announced, “The Midi Muscles In.”

A clear correlation started breaking down during the 1980s, with designers offering a greater range of styles and lengths.

“It used to be that short was in and long was out. If you wore long, you’d be embarrassed,” Marshal Cohen, chief industry analyst at NPD Group, Inc. in Port Washington, New York, said in an interview. “Now you can wear long, you can wear short. You can wear your pajamas to work and no one would care.”

Maxi Return

Yet, even now an occasional correlation can be spotted, Cole said. Last summer, after the S&P fell 57 percent between October 2007 and March 2009, he noticed floor-length sleeveless dresses appearing on the streets of New York.

“There’s a whole generation of young women who’ve never worn a maxi skirt in their lives,” he said.

For her Friday showNicole Miller abandoned her signature figure-hugging dresses in favor of a flowing, layered look that incorporated several hemlines within a single outfit.

“I was just trying to move away from the tight and short,” said Miller, in an interview after the presentation. “There’s no subliminal message there.”

The Guli collection designed by Gulnara Karimova, a daughter of the President of Uzbekistan Islam Karimov, included ethnic Uzbek fabrics, patterns and embellishments applied to floor-length dresses. Toward the end of the event, a group of models strutted out in traditional striped Uzbek robes. Untraditionally, the robes were untied, revealing bodices -- and no skirts at all.