The data these tests rely on are of two general kinds. There are observable data sources, included vote tallies at polling or constituency levels, data on valid and invalid votes, number of valid votes, voter turnout data, but also national registries, including census, national register of birth and deaths, etc. And there are non-observable data sources, which may be hidden from those conducting the analysis, for example, voter registration lists, transmission logs, voter turnout percentages, lists of observers and party agents, access restrictions to polling places, and so on.