Any variable that you're not investigating that can potentially affect the outcomes of your research study
Researcher Bias
The researchers belief or expectations influence the research design or data collection process
Investigator Effects
Researcher unintentionally the outcome of any research they are conducting through non-verbal communication
Investigator simply being there may affect results
Situational Variables
Situational factors other than the independent variable that may cause a result to differ
For example, noise or temperature
Confounding Variables
Extraneous variable that varies systematically with the independent variable so we cannot be sure of the true source of the change to the dependent variable
