In 1980, the econometrician David Hendry (now Sir David) investigated a key economic question: what causes inflation? Hendry looked to the data for insight. He speculated that a particular variable, X, was largely responsible. He assembled data on variable X, performed a few deft mathematical tweaks and compared his transformed X with the path of consumer prices in the UK. Graphing the result showed an astonishingly close fit.

The only snag: X was cumulative rainfall. Since consumer prices and cumulative rainfall both rise over time, Hendry had an excellent platform for finding his spurious correlation. Statistical sleight of hand did the rest.

Hendry wanted to demonstrate just how easy it was to produce plausible nonsense by misusing the tools of statistics. “It is meaningless to talk about ‘confirming’ theories when spurious results are so easily obtained,” he wrote.

All this is by way of preamble, because a hot topic in economics at the moment is the role of finance in the health of the economy. For many years, economists have tended to believe that a larger financial sector tends to be good news for economic growth, with statistical evidence to back this up.

It won’t surprise anyone to hear that this belief is now viewed with some scepticism, and the statistical studies now back up the scepticism too. Several recent research papers have found that finance can be bad for economic growth.

Given this statistical volte-face, Hendry’s conjuring trick comes to mind. Are our statistical studies simply serving as decoration for our existing prejudices?

A recent note by William Cline of the Peterson Institute for International Economics worries that new anti-finance research rests on a statistical illusion. Rich countries tend to grow more slowly than poorer ones. But rich countries also have larger banking sectors. A naive analysis, then, would show that large banking sectors are correlated with slower growth. But, points out Cline, the same statistical methods show that doctors are bad for growth and that telephones are bad for growth and even that research and development technicians are bad for growth. In reality, all that is being shown is that being rich already is bad for further growth.

Cline makes a good point but a narrow one. It’s not particularly helpful to analyse banking like salt in cooking or water on your vegetable patch, and conclude that “some is good, too much is bad”. Unlike salt and water, banking services are complex and diverse. There’s a difference between a mortgage, a payday loan, life insurance, a credit derivative, a venture capital investment and an equity tracker fund. They’re all financial services, though.

More persuasive analyses of the relationship between finance and growth are asking not just whether finance can grow too big to be helpful but what kind of finance, and why.

In two working papers for DNB, the Dutch central bank, Christiane Kneer explores the idea that the trouble with banking is that it sucks talent away from the rest of the economy. Kneer looked at the process of banking deregulation state by state in the US and found that banks hired skilled individuals away from manufacturing, where labour productivity fell. If Kneer is right, too much finance is bad for growth because the banks are gobbling up too many of the smartest workers.

Another possibility, explored by economists Stephen Cecchetti and Enisse Kharroubi, is that large banking sectors aren’t doing their classic textbook job of funding the most productive investments. Instead, they like to lend money to organisations that already have collateral. Mortgages make attractive loans for this reason. Loans to a business that already owns an office block or an oil refinery are also tempting. But lending to a business with more intangible assets, such as an R&D department or a set of strong consumer relationships, is less attractive. Perhaps it is no surprise when Cecchetti and Kharroubi find that larger banking sectors are correlated with slower growth in R&D-intensive parts of the economy. But it is not encouraging.

. . .

Such research reminds us that we shouldn’t simply bash “banking” or “finance” in some generic way, blaming the banks for anything from the weather to the struggles of bees. We need to look at the details of what the financial services industry is doing, and whether financial regulations are protecting society or making things worse.

The truth is that we desperately need a strong banking sector. This entire research literature on finance and growth was originally kicked off by development economists who had observed that poor countries struggled to develop if they didn’t have decent banks. Thorsten Beck, an economist at Cass Business School, first started studying the effects of finance when he worked at the World Bank. “I didn’t care about the UK or the Netherlands. I cared about Kenya, Chile and Brazil.”

Without a strong and sizeable banking sector to lend money to businesses, it is very hard for a poor country to grow. It may well be that we have more finance sloshing around the economy than we can use. That is a big problem — but it is also a first-world problem.