On the level of the variables which are included on a certain reporting form, the following changes have to be managed by the SAPHMIS, in order to enable longitudinal analysis:

• A new variable can be created or an existing variable can be deleted. This happens due to changing information needs. An administration might e.g. decide to remove a lot of variables in order to streamline the HMIS. The removed variables may not be visible for the future reports. But they can not simply be deleted, since this would mean a loss of entered data from the old reports.
• Two or more variables can be merged to one. Also, one variable can be split into two or more. This happens, when a certain data item is needed in a lower or higher degree of detail. For the reporting of treated diseases it might be decided, that it is no longer necessary to report the cases by sex, which merge the two variables for each observed disease into one variable. If values from the resulting variable will have to be compared to values which were entered before merging, the old values have to be summarized accordingly.
• The scope of a variable can be broadened or narrowed. This means a redefinition of the variable which systematically includes more or less cases. E.g. it might be decided for a vaccination program, that there is no more need to report completely vaccinated children which are older than one year. If not respected in a longitudinal analysis, this would result in a false interpretation of the decline of cases.