Pollster: When opinion researchers need a population sample that reflects the demographic characteristics of the national population, they choose their sample on the basis of national census data  Not everyone participates in the national census, despite its being mandatory  If, however, census participation became voluntary, as some have proposed, the participation rate would be much lower
So if census participation became voluntary, polls designed to discover the opinions of the national population would have less accurate results
Among people who do not currently participate in the national census, few, if any, would agree to participate if participation were voluntary.