Strata, subset

[Braventos]

At the moment estimates can be stratified or calculated within a subset of the population using separate functions (getPSSAStrata and getPSSASubset) which in turn use generateDenominatorCohortSet from IncidencePrevalence. We could try to merge this functionality in the main function (getPSSA) by adding ageGroup, sex, and the name and id of the subset table (previously instantiated). If we do that, it makes more sense to restrict getPSSA() to only reference existing tables (see Issue #9).

@edward-burn @xihang-chen

[edward-burn]

This could also look a little like the strata option in cohortSurvival where users can stratify on a variable they have added externally (eg using addDemographics from patient profiles)