What is social desirability?
Social desirability is the tendency of an individual to describe him/herself positively, to respond to questionnaire items in a way that may affect the validity of his/her self-assessment, to choose a response that is considered favourable by society or a response that is as moderate as possible.
This can be done by maximizing "good" (desirable) behaviours or minimizing "bad" (undesirable) behaviours.
Candidates may answer social desirability questions in a manner that conforms to the employer's anticipated expectations rather than in a manner that is representative of their actual behaviours. Therefore, strong social desirability may be motivated by a need for approval and sympathy.
A person with a high score might present themselves in a favourable manner to please others, however, there is also the possibility that their responses reflect their true nature (a person with all the "desirable" behaviours). At this point, since there is no way to distinguish between the two types of behaviours, the high score is nothing more than a social desirability index, a signal to be more vigilant and to probe further during the interview process.