The correlation between skirt lengths and economic booms and busts - the so-called hemline index - is not only well documented but even seems to have stood the test of time. In essence, short skirts are a sign of confidence and a precursor to rising stock markets; while longer lengths signify caution and a market downturn.

But now it seems heel heights have something to say about the state of the economy too. A new study by IBM suggests that instead of heels getting higher, as is usually the case in a recession, this time women are turning to lower-heeled shoes as the global downturn drags on. The implication, it says, is that shoppers may be knuckling down for "long-term austerity."

IBM's findings come after it monitored billions of social media posts. And they certainly fly in the face of trends seen over the last 100 years, when heel heights soared during the most prominent recessions in US history.

Low-heeled flapper shoes in the 1920s were replaced with high-heeled pumps and platforms during the Great Depression. Platforms were again revived during the 1970s oil crisis, reversing the preference for low-heeled sandals in the late 1960s. And the low, thick heels of the 1990s "grunge" period gave way to "Sex and the City"-inspired stilettos following the dot-com bust at the turn of the century.

But in a potential deviation from this long-term trend, an analysis of the last four years of social media showed that discussions on increasing heel height reached a peak towards the end of 2009 - but have been declining ever since.

For example, between 2008 and 2009 footwear bloggers wrote regularly about heels from five to eight inches, but by mid 2011 they were heralding the return of the kitten heel and the perfect flat from Jimmy Choo and Christian Louboutin.

Of course this is not to say that the sky-high heels have disappeared altogether - as a visit to any shoe store will confirm. Instead, as the economic downturn has worn on, they are discussed as glam-wear instead of for the office or shopping trip.

The analysis was carried out using special analytics software to search billions of social media posts to identify individuals discussing shoes. Not surprisingly, this initial category contained tens of thousands of posts.

Next, the software narrowed the list down to what IBM describes as key online 'influencers' in the footwear arena - bloggers, for example. The software used special algorithms to rate the popularity of these influencers by zeroing in on the ones who sit in the centre of large social networks - that is, writers of blogs that many other blogs link to and which in turn link to many blogs. These bloggers aren't traditional 'experts' - they don't work in the footwear industry, for example. But they are passionate footwear enthusiasts with large followings.

Finally, the software analysed the content of the social media sites, looking specifically for discussions of shoe height.

So what does this all mean in the real world? Apart from an eye-catching headline, IBM says its analysis of social conversation in real-time points to a change in trend. And this data could in turn be a key tool for manufacturers and retailers looking for insight into the kind of products to make and sell in the coming season.

It's certainly food for thought. Businesses are increasingly using social media and the internet, to engage with shoppers - indeed, a survey by the US-based National Retail Federation (NRF) last week said more retailers than ever before are set to use social media to connect with shoppers this holiday season, especially when it comes to highlighting discounts and promotions.

But how many of them actually factor information from blogs and other forms of social media into their strategic decisions?