Statistics should do more than measure something at one point. To be useful, statistics should also be able to constitute a basis for comparison.
Such comparisons might measure a change over time. For example, the number of households with access to a tap in 1996 compared with the number in 2001.
Or they might measure the same variable in different areas withina country. For example, the percentage of people employed in each of South Africa's nine provinces compared with the percentage in the country as a whole.
In some cases, statistics can measure variables across countries. For example, the rate of change in consumer inflation in France in July 2004 compared with the equivalent rate in South Africa for the same month.
To be meaningful, these sorts of comparisons must be based on equivalence. In other words, like must be compared with like.
In statistical terms, this necessitates the use of common standards, classifications and definitions. Failing this, the basis of comparison will be flawed.
This goes to the heart of the often-repeated confusion over the two definitions used in the measurement of unemployment in South Africa.
The distinction between these two measures is more than just semantic.
In the official definition, the unemployed are those people within the economically active population who: did not work during the seven days prior to the interview; want to work and are available to start work within two weeks of the interview; and have taken active steps to look for work or to start some form of self-employment in the four weeks prior to the interview.
In the expanded definition, the third criterion (some sort of work-seeking activity) is dropped.
The expanded definition will therefore include, as unemployed, those who might be termed "discouraged job seekers".
This would cover those who said they were unemployed but had not taken active steps to find work in the four weeks prior to the interview, perhaps because they did not feel they had any chance of obtaining work, or because the costs of travelling from home to an area where work might be available were prohibitive, or because of an absence of transport from home to an area where work might be available.
Many discouraged job seekers will be found in rural areas distant from the major cities and towns.
The difference in measurement, depending on which definition is used, can be substantial.
For example, in the March 2004 labour force survey, the results of which were released at the end of September, 27.8 percent of the economically active population was unemployed. On the expanded definition, this rose to 41.2 percent.
The International Labour Organisation uses the official definition of unemployment as its basis for comparison of labour market statistics between countries. That is why Stats SA collects data on unemployment using this definition.
However, in countries with high rates of unemployment, and uneven economic development between and within regions and provinces, the official definition is likely to exclude substantial numbers of discouraged job seekers.
That is why Stats SA also collects and reports on data using the expanded definition.
Some callers to a recent talk radio show on this subject suggested Stats SA was part of a conspiracy to hide unemployment by using the official definition, and did not seem aware that unemployment was also reported on using the expanded definition.
Others criticised Stats SA for not taking account of discouraged work seekers in its measurement of unemployment, failing to note that this is precisely what is done using the expanded definition. There is no conspiracy in the way Stats SA's labour force survey measures, and reports on, unemployment.
This is undertaken in two different ways, both of which are presented clearly, and are based on transparent and established methodologies.
Stats SA's way of reporting on unemployment both facilitates comparison with other countries, while also taking account of the socioeconomic circumstances that might create a large number of discouraged job seekers not included as unemployed under the official or narrow definition.
Pali Lehohla is South Africa's statistician-general and head of Statistics SA. For more information on Stats SA and its statistical outputs, including the most recent labour force survey release, visit www.statssa.gov.