Investigator effects

• Reduces the study’s ecological validity
• Many characteristics- researcher‘s age, gender, accent or clothing can influence participant responses.
• Eg in an interview about sex, females may feel less comfortable answering questions asked by a male interviewer and thus give different answers than if they were asked by a female. The researcher‘s biases may also come across in their body language or tone of voice, affecting the participant‘s responses
• In some study designs, researchers can control for demand characteristics using double-blind methods
• Double blind methods example- neither the pps nor the researcher know which pps get the actual drug and which get the placebo, this way the researcher is unable to give any clues to participants that would affect their behaviour