Surveys with data all reported by the same person may be somewhat biased because of which of the following reasons?

Surveys that rely solely on data reported by a single individual can introduce biases primarily due to social desirability and shared method variance. Socially desirable responding occurs when respondents provide answers that they believe are more acceptable or favorable to others rather than what they truly believe or experience. This can skew results and lead to an overestimation or underestimation of certain attitudes or behaviors.

Shared method variance is another factor that can influence the bias when the same respondent answers multiple questions. It refers to the variance that is attributable to the measurement method rather than to the actual relationships between the constructs being measured. When responses are sourced from a single person, the likelihood of consistent bias across different answers increases, which can compromise the reliability and validity of the data collected.

This combination of social desirability and shared method variance makes the responses less reflective of reality, as they may not accurately capture the true behaviors, attitudes, or experiences of the individuals surveyed. Therefore, relying on a single respondent's reports can lead to an overly optimistic or pessimistic view of the subject being studied, undermining the study's findings.