GDP: something loosely related with output and welfare

Via João Pinto e Castro e na sequência do que aqui se escreveu sobre o PIB per capita regional, chego a este artigo de John Kay (“Why data, soft or hard, cannot replace eyes and ears”) publicado no Finantial Times do qual retenho o seguinte excerto onde se fala, a dada altura, do Produto Interno Bruto (ou GDP em inglês) – sublinhados meus:

Last week, the Conference Board announced that European labour productivity growth had overtaken that of the US. The news that growth in Europe in 2006 was 1.5 per cent against 1.4 per cent across the Atlantic was the main headline in this paper.

While the reputation of economists has been in decline, naive acceptance and popular distribution of economic statistics has grown. Figures such as these are taken at face value, as if they were established facts. Markets tremble when an announcement differs from expectations by as little as a single decimal point.
But the margin of error in such data is an order of magnitude larger than these differences.
Sampled data may not accurately represent the population. But there is a larger and more subtle problem: the difficulty of translating broad economic concepts, such as national income or productivity, into something that can be measured.

In all areas of human endeavour, there are hard data and soft data. Once you determine a scale for temperature, Fahrenheit or Celsius, every competent observer will arrive at the same answer. But the attractiveness of a face, the happiness of a society, the progress of a civilisation, is multi-dimensional: components of attractiveness, happiness or progress are determined by subjective consensus and are not susceptible to objective measurement.

(…) Output seems like a hard number – and would be if it were simply a matter of counting the widgets that leave a production line. But the output of a modern economy is made up of thousands of differentiated products of changing quality and composition. The US productivity miracle was in part created, not by finding new facts about the US economy, but by reclassifying software expenditure as investment and adopting aggressive assumptions about falling computer prices.

The key number used to measure economic performance is gross domestic product. But few politicians or traders could actually define it. GDP is not, exactly, a measure of either business output or consumer welfare, although it is loosely related to both. It is safest to say that GDP is the number you arrive at if you follow an internationally agreed set of statistical conventions.

So long as everyone follows these conventions, movements in GDP tell you something about national prosperity and economic progress, even if it is not entirely clear what. But no economic data, hard or soft, can ever tell the whole story. Prosperity and progress are soft concepts and official statistics are at best a supplement, not a substitute, for evidence of eyes and ears. (…)”

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