The sampling functionality is accessible through the Sampling tab within the Report Painter Report Options dialog box in Developer Studio or in the Sampling function within the Modeling tab in App Studio. There are three sampling techniques: Random, Numeric Stratified, and Categorical Stratified.
When you sample a population, stratified sampling allows us to ensure that the proportion of each stratum in the sample is the same as in the population. Numeric stratified sampling is used when the field identifying the strata is a number and can be defined in terms of a range. Categorical stratified sampling is used for all other data.
Accessing sampling criteria requires that at least one field is defined within the report extract. If no fields have been defined, you will receive a warning message informing you that no fields are available for sampling and the Sampling tab will be present, but no actions will be available. For Random Sampling, which is not tied to a specific field value, any field will open the option. For Stratified sampling, the stratum field (the field on which the strata will be defined) must be included in the report.