Suppose you want to know how often people brush their teeth every day, so you take a survey. Explain why the survey results would indicate far more gleaming smiles than actually exist. (In fact, such a survey would indicate about twice as much brushing as actually happens.)
I assume that this question is saying that people are claiming that they brush their teeth twice as much as they actually do. The reason why the survey would find this is that people do not always answer surveys truthfully. This is one major reason why survey results can be inaccurate.
In surveys, people are generally asked to report on their own behavior. The behaviors that they report are not verified by anyone. This means that they do not have to be truthful. When people have the chance to report on their own behaviors and cannot be checked up on, they will tend to report behaviors that they think they should engage in, not the things that they actually do. In this case, people are saying that they brush their teeth more often because they know that is what they are supposed to do. They know that brushing their teeth is a good thing to do and so they want to tell others (the survey takers) that they act in the proper ways.
Thus, this survey will result in exaggerations of how much people brush their teeth because the respondents want to report behaviors that make them look good, not the actual behaviors in which they engage.
When conducting survey, a researcher asks a participant some questions. Let's say a researcher wants to know how often do people brush their teeth. Brushing one's teeth is listed as a personal hygiene. It has been said that you should brush your teeth three times a day. If anyone was asked about that matter, that individual might or might not tell the truth. Of course, to most people, it is such a shame to confess or admit that they do not brush their teeth as regularly needed especially when you're talking to a person you don't even know like that of a researcher. Everyone wants their name to smell so good that they would even lie thinking that it would make them a better person than telling the truth.