Aggregation

Aggregation is a method that involves merging study domains or response categories. It can be used for both frequency tables and magnitude tables. The method leads to a decreased level of detail in the statistics and to different classifications being reported with different levels of detail.

Cell Key Method (CKM)

The Cell Key Method (CKM) is a method used for frequency tables and makes it possible to report detailed statistics without having to hide statistical values or make parts of the table less detailed. The method supplements table values with a small and controlled amount of random uncertainty in connection with the preparation of statistical values, without creating any bias in the statistics. The method implies that no individual consideration of risk assessment is necessary.

Statistical values that are greater than zero are either adjusted by a small negative or positive integer or left unchanged. All totals are adjusted in the same way. One consequence of the method is that the reported totals are not always equal to the sum of their reported components. For example, the reported totals for women and men do not necessarily correspond to the sum of the reported statistical values for women and men, respectively.

The uncertainty added is small, but the impact is greater for low frequencies than for high ones. This also has a bearing on proportions, which should always be interpreted with caution when based on low frequencies.

If reported statistical values are added together to create a new total, the uncertainty is also added. There is therefore a risk that the new total contains greater uncertainty than that which – under the method – would have been added to a single value.

Rounding

Rounding is a method that adds noise. It is suitable for frequency tables. There are different ways of applying rounding; generally, random rounding is recommended. Depending on how much rounding is used, the uncertainty can be relatively large, especially for small values. Depending on how totals are produced, it may also be that when rounding, the reported totals are not always equal to the sum of their reported components.

Suppression

Suppression is a protection method often used for magnitude tables, for example in business statistics. The method means that cells with a high risk of disclosure are hidden (primary suppression). Other cells are subsequently also hidden (secondary suppression) to avoid the possibility of deducing the primary suppressed cells via marginal cells. If the statistics are presented with many different classifications, extensive secondary suppression may be needed to protect a small number of primary suppressed cells, which can result in a relatively large loss of information.