When the age of the researcher influences the behaviour of the study participant, it is called:

When the researcher's age shapes a participant's behaviour, it is a biosocial effect stemming from a visible personal characteristic.

Sociological impact is too broad and does not name this specific biosocial source.

Psychological impact refers to internal mental states, not the researcher's biological traits.

Psychosocial effect concerns the participant's own combined mental and social response.

Biosocial attributes include age, sex and race of the experimenter that can bias responses.

Awareness of such effects guides matching or standardising researcher characteristics.