Before a pollisreleased, pollstershavetodosomeworktomakesurethesamplesizelooksjustliketheentirepopulation, basedonsourcesliketheUSCensusandvotingfiles.
Soifeachindividualin a pollstartsoffwith a valueof 1, weightingiswhenpeoplewhoareunderrepresentedcomparedtothelargerpopulationget a valuehigherthan 1, whilegroupswhoareoverrepresentedget a smallervalue.
Theyrepeatthisforfactorslikeage, andrace, andgeographiclocationtoo, untileachindividualisweightedin a waythatmakesthesample a goodstand-inforthelargerpopulationitrepresents.
Butfor a polltobe a precisepredictionofanelectionoutcome, pollstersareattemptingtoweightagainstanunknownpopulation, thepeoplewhowillactuallyvoteinthefuture, onelectionday.