Which aspect of the researcher may cause psychosocial effect in the participant of a study?

The researcher's attitude is the aspect that can create a psychosocial effect in participants.

Psychosocial effects stem from attitudes, expectations and manner conveyed to the participant.

Age is a biosocial characteristic of the researcher, not a psychosocial one.

Race is likewise a biosocial attribute affecting behaviour through social perception.

Sex too is a biosocial feature of the researcher rather than a psychosocial state.

Experimenter expectancy is a classic psychosocial source of bias in behavioural studies.