Standardisation – explanation and calculation

When is it necessary to standardise the current indicators?

How common is a given disease? How high is the hospitalisation rate? What are the costs to the health care system? Many health and health care indicators are only meaningful in comparison if the size of the population to which they refer is known. For this reason, rates are calculated to present the numbers per 1000 or 100 000 inhabitants (crude rates).

In addition to the population number itself, further characteristics of the population are important. First and foremost are age and sex structure. One can expect, for instance, that in a very elderly population, certain diseases will be more common and that hospitalisation rates and the costs of the health care system will be higher. Or women of childbearing age, for example, will be seen to have more hospital stays than men of the same age.

Major differences in a population’s demographic characteristics can be seen in particular in a global context. But there are also differences between Switzerland’s cantons. For example, in 2019, the population of the canton of Ticino with 23% aged 65 or over, was considerably older than that of the canton of Fribourg (16% 65+ year-olds). Changes to the composition of a given region’s population can also take place over time.

If differences in composition are not taken into account, it can lead to distorted conclusions. These can be avoided through standardisation. Standardisation is a calculation enabling structurally different populations to be compared (e.g. in space or time). With standardisation, simple, intuitive access to the effective numbers is lost at the same time.

A standardisation leads, for example, to a reduction in the mortality of the canton of Ticino in 2018 from 892 to 738 deaths per 100 000 inhabitants. In the canton of Fribourg, standardisation leads to an increase in the rate from 646 to 814 deaths per 100 000 inhabitants. The higher crude (non-standardised) rate in Ticino can be explained by the older population compared with Fribourg. If both population groups are based on the same demographic composition (here the European standard population in 2010), the comparison shows lower mortality in Ticino.

How does Obsan standardise indicators?

Standardisation is carried out using the direct method. This means that group-specific rates (by age and sex) are calculated and weighted, so that they are adapted to the population composition of a theoretical standard population. The results can be compared with the results of other populations, but the converted results bear no direct (intuitive) relationship to the number of cases.

Formula for the calculation of age and sex-standardised rates (R) :

R : Age and sex-standardised rates
Nij : Number of persons in age group i and sex j in the standard population
rij : Age and sex-specific crude rates of the examined population
The European standard population in 2010 (Eurostat, 2013) is used as the standard population.

The confidence interval, which is also shown, is a measurement of the estimate’s accuracy. It defines the limits within which the true value can be found with a probability of 95%. The standard error and 95% confidence interval are calculated based on a gamma approximation of the variance in the rate (Tiwari et al., 2006).

Where can the crude rates be found?

Although the crude rates no longer appear in the graphics, they can be found in the data tables, which can be opened by clicking on the relevant button.


  • Eurostat (2013). Revision of the European Standard Population — Report of Eurostat's task force. Luxembourg: Publications Office of the European Union, p. 121. Report.
  • Tiwari, R. C., Clegg, L. X., & Zou, Z. (2006). Efficient interval estimation for age-adjusted cancer rates. Statistical methods in medical research, 15(6), 547-569. Publication.