Fed chair Janet Yellen. Photo: Reuters

This week, the Federal Reserve and the Bank of England (BoE) made welcome moves towards more simplicity. Specifically, they recast the “forward guidance” they’d previously given investors about their intentions.

Both central banks have been surprised by unexpectedly rapid falls in unemployment.

The Fed had previously promised not to start raising interest rates before unemployment in the US had fallen to 6.5 percent. At 6.6 percent, it’s almost there – but recovery is still weak and the Fed has no intention of raising rates for a while.

The BoE’s unemployment threshold was 7 percent. That’s probably already been reached, but the UK will most likely need low interest rates for months to come. It was a mistake to make specific rates of unemployment “thresholds” for adjusting monetary policy.

The state of the labour market is crucial for judging policy, but it isn’t the only factor; in any case, the headline rate of unemployment doesn’t accurately measure labour-market conditions. US unemployment has fallen rapidly partly because workers are quitting the labour force, not just because they’re getting jobs.

There’s plenty of room for the UK’s economy to grow, despite the unexpectedly rapid fall in unemployment. In both countries, adding unemployment rates to the guidance was meant to support demand by convincing investors that interest rates would stay low for longer.

This was the right objective under the circumstances. Then the unemployment measure started getting smaller – and investors began to get confused.

Rather than clarify their guidance, thus making it even more complicated, new Fed chairman Janet Yellen and the BoE’s Mark Carney rightly chose to make it simpler.

Carney’s new formulation omits the unemployment rate altogether, and he says instead that the bank “will not take risks with the recovery”. There’s plenty of spare capacity, he said, and even when that starts to run out, the bank will raise rates slowly and cautiously. The BoE also published more information on its economic forecasts than it has before, showing it expects rates to stay put until mid-2015.

Yellen wasn’t so forthright in abandoning the Fed’s unemployment threshold, but what she said amounts to the same thing.

The fact that headline unemployment is close to 6.5 percent tells investors nothing – and that’s official. She said the Fed is looking beyond traditional measures of unemployment to judge the tightness of the labour market and detect any incipient pressure on inflation. This new balance makes sense.

Give investors more information and explain the thinking more fully – but don’t tie policy to specific indicators, and don’t make promises (or seem to make promises) you don’t intend to keep.