Over recent weeks global equity markets have maintained an upward bias despite worries in some quarters regarding the sustainability of the current upturn.

One of the most significant recent pieces of economic data that acted to encourage the bulls was the US employment report for September. Employment in the US grew by 57,000, which was the first positive monthly figure since January, and compared with expectations of a decline of 20,000.

Although care needs to be taken in interpreting one month's figure, this employment report took on more than usual significance because it may signal that the US economy is on the cusp of delivering a sustained increase in jobs.

So far in 2003 the US economy has been growing at a healthy clip but this has been accompanied by continued deterioration in the labour market. This has led to fears that the economic recovery may not be sustainable.

In particular, consumer expenditure, which remains the mainstay of the US economy, requires new jobs to support consumer confidence.

Fears of a "jobless" recovery underlie much of the scepticism that surrounds the likely strength of the US economy going into 2004.

The figures for September also included a very large revision for the August payroll figure that initially showed a drop of 93,000, but was revised to a much more modest fall of 41,000.

Taking this revision into account provides more support for the view that US employment levels are now likely to grow in coming months.

Consequently, the October and November US employment reports will be watched very carefully by market participants and have the potential to have a large impact on market sentiment.

The dangers, however, of relying heavily on one or two economic data releases have long been apparent. Regular releases such as the US monthly employment report are usually subject to revisions.

Therefore, even for an economy such as the US where economic data is available on a timely basis, it can be very difficult for economists to get a true picture of the economy.

Market analysts and economic and monetary policymakers have learnt to live with this variability in the quality of economic statistics.

Therefore, three- or six-month trends in economic series receive much greater attention than the actual monthly numbers.

The pitfalls associated with economic forecasting and policymaking were, however, highlighted as a result of recent revisions concerning the British economy published by the UK National Statistics Office.

The revisions to the UK National Accounts data incorporated a new method of weighting the different sectors of the economy and at the stroke of a pen dramatically altered the picture of the recent performance of the UK economy.

UK GDP estimates for the first and second quarters of 2003 were doubled compared with previous estimates.

For the more volatile business investment series, the second quarter figure was revised to plus 2 per cent, sharply higher than the -1.1 per cent in the initial estimate.

This resulted in a revision to the year-on-year figure to -0.7 per cent from the previous estimate of -3.5 per cent.

On the basis of this new information business investment in the UK would seem to have held up much better than earlier estimates over the past 12-18 months.

For the Bank of England's monetary policy committee (MPC), which is charged with formulating monetary policy and setting interest rates, this new data is bound to lead to a reassessment of the appropriateness of the current level of British interest rates.

The official UK short-term interest rate was lowered to 3.5 per cent over the summer because the MPC was convinced that the economy was in a fragile state.

It now seems that the economy was in fact in quite good shape and consequently may not have needed that final cut in interest rates.

One positive aspect of the revised data is that it shows that the British economy is performing in a more balanced fashion than that indicated by the earlier estimates.

The MPC had been concerned that private consumption had been growing too fast fuelled by a boom in house prices and associated remortgaging activity. The revised figures show that private consumption has not been as strong as previously thought and that the business sector has in fact been performing much better than the older estimates.

Those involved in analysing the Irish economy and in formulating economic policy have had to learn to live with many difficulties in the depth and quality of Irish economic statistics.

The open nature of the Irish economy and the trading activities and accounting policies of multinational companies can play havoc with the national accounts data.

The recent UK experience shows that even in the bigger economies great care needs to be taken in assessing the economic data.

Even though some Irish economic statistics need to be treated with some scepticism, it is clear that this is a problem that is not just confined to Irish economic data.