In an honest poll, they attempt to make their sample indicative of the overall population. For example, if a poll were in a State where 60% of registered voters were democrat, then 60% of those polled should be democrats. In California, democrats outnumbered republicans 2 to 1 in the last presidential election. So a reasonable poll of California would be to ask 66% democrats and 33% republicans. Not that pollsters are unbiased, but over/under sampling to reflect the actual overall population is a legitimate and logical practice.
In an honest poll, they attempt to make their sample indicative of the overall population. For example, if a poll were in a State where 60% of registered voters were democrat, then 60% of those polled should be democrats. In California, democrats outnumbered republicans 2 to 1 in the last presidential election. So a reasonable poll of California would be to ask 66% democrats and 33% republicans. Not that pollsters are unbiased, but over/under sampling to reflect the actual overall population is a legitimate and logical practice.