People tend to present themselves in a positive light when they are in a research study. This is especially true during face-to-face and telephone interviews on subjects like religion and socially desirable activities like voting.
They also admit to less participation in socially undesirable activities like substance abuse or holding racist and sexist opinions.
When people answer surveys based on desirable rather than actual behavior, a social desirability bias exists.
Pew Research finds that self-administered surveys likely reduce social desirability bias compared to surveys based on interviews.
