1.2 A statistic describes a closely demarcated object

For purposes of measurements that cover large groups, one has to narrow down the perspective. In order to obtain reliable measures, it has to be agreed in advance what exactly the measured unit describes. A statistic always describes a concept defined in advance. For example,

The concepts have many tasks. First, they define the object of study. A set of statistics may describe cities, buildings or people, for example.

The concepts also determine which aspect of the object is highlighted in the statistics. The population may be classified in statistics into different social groups, for instance. The classification may be based on level of education, occupational status or income. The boundaries between different classes may also be defined in different ways. The classification applied determines the aspect that is considered important.

Statistical concepts also determine how different things are related to one another. For purposes of measuring price increases, for instance, it is necessary to determine in advance the weights of the prices of different products. It has been agreed that housing costs have great importance to the overall increase in prices, whereas health care costs have only little importance. This agreement is based on research findings which show that, on the average, people spend large sums on housing but fairly little on health care.

Concepts are usually defined in such a way that they meet certain information needs. The rate of inflation, for example, tells consumers how price levels and their costs have developed. Most important in this regard are housing costs and food prices.

From the point of view of a different kind of information need, this concept gives the wrong picture. For example, the costs of a production unit develop in a completely different way from those of an individual consumer. It is more important for the production unit to know how wages and the price of energy have developed.