My opinion is based on the body of research carried out. I do a lot of quantitative analysis. The response rate for surveys we use and administer in ordinary conditions is steadily declining. A few years ago, approximately 75% of the population answered questions for an ordinary survey. Today, a response rate of 50% is considered to be good. And yet, it is clear that an entire segment of the population is underrepresented. This cannot happen with the census.
