It is said hemlines fall in a recession, while shorter skirts signify the heady optimism of buoyant economic growth.
But a new study suggests that the fashionable length to have your hemline fluctuates in a 20-year cycle, with no link to the ups-and-downs of a country’s fiscal fortunes – meaning it is always worth hanging on to outdated clothes.
While hemlines were demure in the 1950s, epitomised by Grace Kelly, they rose significantly in the 1960s and 1970s, as Mary Quant introduced the miniskirt.
Grace Kelly is the model of demureness in an ankle-length dress in 1949
Skirts then fell to calf-length again by the 1980s – a trend widely embraced by Diana, Princess of Wales – and fell further in the 1990s, illustrated by Gwyneth Paltrow’s popular floor-length maxis.
Research by Northwestern University, in Illinois, suggests that if the current pattern holds, then midi-skirts, which reach mid-calf, will be out of fashion by the 2030s, replaced by floor-length alternatives.
So although it may be tempting to donate or throw away unstylish garments, the science suggests they will eventually return to the runway, and subsequently, the high street.
Prof Daniel Abrams, co-director of the Northwestern University’s Institute on Complex Systems, said: “Over time, this constant push to be different from the recent past causes styles to swing back and forth.
“The system intrinsically wants to oscillate, and we see those cycles in the data.”
Researchers said that fashion was constantly in tension between wanting to stand out, while also wanting to fit in.
Once a style becomes too common, designers move away from it, but not so far that the clothes become unwearable.
The analysis was done by US researchers, who developed a mathematical model to analyse 37,000 images of women’s clothing from magazines and sewing patterns between 1869 and today.
Gwyneth Paltrow helped popularise the floor-length maxi in the late 1990s – Everett Collection Inc/Alamy Stock Photo
They discovered that clothing trends germinate, and grow in popularity, peaking around 10 years after they first appear, before gradually falling out of fashion and being outdated within two decades.
Dr Emma Zajdela, of Princeton University, said that in the next decade, they expected trends to be similar to those in 2010, with midi skirts “on the way out”.
George Taylor, an economist, was the first person to suggest that hemline length followed a pattern, but he believed it was linked to economic prosperity.
In 1926, he proposed “The Hemline Index”, suggesting that the length of skirts rose and fell with the country’s circumstances.
For example, the boom-time of the “Roaring 20s” was categorised by the scandalous “flapper” style, as skirts rose shorter than ever before.
In contrast, floor-length dresses and trousers dominated fashion during The Great Depression.
The same cycle plays out despite the swinging economic pendulum
But the new study suggests that this was coincidental and the same cycle plays out despite the swinging economic pendulum.
Researchers found that the same 20-year rule also held true for waistlines and necklines.
As hemlines were becoming longer in the 1930s, necklines also became more modest, before plunging in the 1950s, as seen on Hollywood sirens such as Rita Hayworth or Sophia Loren.
Likewise, the higher necks of the late 1960s and 1970s coincided with longer hemlines before falling again in the 1980s.
Mary Quant helped usher in the Swinging Sixties with the miniskirt and hotpants – Sjoberg Bildbyra/Getty Images
Currently, necklines are on the way down from a recent modest peak at the end of the 2010s.
Dr Zajdela said: “We see similar patterns in our data of approximately a 20-year cycle for necklines and waistlines, although they are not necessarily in sync with each other.
“There are of course many dimensions of fashion – patterns, shape, fabric – that could be analysed and would perhaps show a similar cyclical pattern, although our data doesn’t include these measures.
“Anecdotally, for example, leopard print, which recently gained popularity, has come back in fashion several times.”
However, researchers say the pattern has lost its clarity in recent decades, with a wider range of skirt lengths appearing from the 1980s, suggesting that trends are becoming more fragmented.
“In the past, there were two options – short dresses and long dresses,” added Dr Zajdela.
“In more recent years, there are more options: really short dresses, floor-length dresses and midi dresses. There is an increase in variance over time and less conformity.”
The research was presented this week at the American Physical Society’s Global Physics Summit in Denver.