The Statistician is an innocent found in every Disgaea game except for Disgaea 2: Cursed Memories as they were replaced by Felonies. They increase experience depending the value of the Statistician (i.e. a 30 Statistician would increase EXP by 30%). They are capped at 300 each and it is NOT possible to create multiple stacks of Statisticians for fast leveling (for example, 32 stacks of 300 Statisticians would still yield 300% EXP) In later games (Disgaea 2, 3 and so on) this trick works??? and makes it possible to reach Level 9999 in two fights at Land of Carnage House of Ordeals 4). In Disgaea 3 and 4, they are found through Reverse Pirating.
Statisticians in Disgaea: Hour of Darkness are capped at 300% the EXP gain total, combined across all Statisticians in all equipped items. To create multiple stacks in later games, use the Puppy Paw Stick to duplicate an Item with a Statistician and fuse them until there is a 300 one before making multiple stacks.
The effective cap for Statisticians in Disgaea: Hour of Darkness is 300% (though the max for a single Statistician is 600), in Disgaea 3: Absence of Justice, it is 9600%, in Disgaea 4: A Promise Unforgotten and Disgaea D2: A Brighter Darkness, it is 4900%.