Comparing countries often leads to controversy, especially when the statistical methodologies used to measure each country are themselves the object of debate. Such is the case in respect of the UN's Human Development Report.
One of the better-known tools for cross-national measurement is the UN's human development index (HDI), a composite made up of a life expectancy index, an educational index (combining adult literacy rates with primary, secondary and tertiary enrolment), and a gross domestic product index (using per capita purchasing power in US dollars).
While the index represents an advance over purely economic comparisons, it is still unable to capture the complexity of national development processes and compare these across countries.
To some extent, this is because it is based on a small number of indicators. By comparison, the monitoring of the millennium development goals is based on a far wider range of statistical indicators and data sources.
Questions have been raised about the sources, reliability and consistency of some of the data used in computing the HDI. In this regard, the statistician-general tabled misgivings at the UN Statistics Commission in March in response to the Human Development Report released in 2004.
Views on the usefulness of the index differ markedly. Amartya Sen, a Nobel laureate in economics, treats the HDI as a major source of information enabling understanding of the social and economic world.
On the other hand, David Henderson, the former head of the economics and statistics department of the Organisation for Economic Co-operation and Development, has argued that the index offers a false perspective on world affairs.
In 2000 the UN Statistics Commission convened to consider a critique of the HDI by Ian Castles, a former Australian commonwealth statistician.
His criticism centred on how international comparisons of economic statistics could be produced when each country estimated economic performance using its own currency.
Several of his criticisms were found to be justified, especially in respect of material errors in statistical accuracy, and the choice of data used to compile the HDI.
A more fundamental critique has been developed by Jacob Ryten, a former deputy head of Statistics Canada, who is advising Statistics SA on economic measurement.
He argues that an index that purports to measure the sum total of human endeavour cannot aptly be reflected in a single index, and urges statisticians not to use single numbers to articulate complex social changes.
He adds: "If the choice is to mislead with a single figure or to explain awkwardly with six, the latter should be professionally if not emotionally preferable."
Such questions are pertinent in evaluating the latest HDI report, which concludes that conditions of life in South Africa have deteriorated.
Data used to calculate South Africa's ranking in the 2005 HDI have been drawn from mostly unofficial sources, extracted from pre-2003 statistics.
Data have also been recycled: if information is not available for the year in question, it is derived from other periods without the extrapolation methods being made explicit.
For example, when the report was released, the official mid-year population estimates were already available. Without explanation, the report ignored the mid-year estimates of an infant mortality rate of 43 per 100 000 people, quoting instead a rate of 53 per 100 000.
Equally, South Africa's maternal mortality ratio was estimated at 55 per 100 000 in 1997, rising to 78 in 2001, and declining to 73 in 2002. Yet the report asserts that South Africa's maternal mortality ratio is 230 per 100 000 people.
This does not imply that the HDI should be ignored or rejected. It is part of the battery of tools for monitoring development. There is, at present, no suitable alternative for measuring human endeavour.
However, precisely because of the lack of alternatives, it is important to be exceedingly cautious when applying this indicator.
The statistics used for cross-national comparison, not just in the computation of the HDI but also in analysis undertaken by international agencies, are sometimes drawn from such diverse sources that they should not be used in the same analysis.
For example, one agency recently drew mortality and fertility rates from one source, but used population estimates from another data source. But population estimates have to be based on projected mortality and fertility rates, and these cannot be separated.
Analysis and comparison cannot simply choose those statistics that support an argument or pre-determined assessment. In today's global information order, statistics are often accepted as providing an almost definitive profile of a country.
When these quantitative facts are incorrect, they mislead. When they are erratic, they misinform. When such mistakes are not corrected, they create doubt and mistrust.