The first type is situational variables, which include the environmental aspects, such as lighting conditions, temperature, and wind, affecting the subjects’ behavior. These aspects need to be controlled so that all the conditions are the same for all participating groups, for example, by using standardized instructions. Therefore, situational variables can affect the outcomes of the research, and they need to be controlled to ensure all participating groups are standardized.
The second type is the experimenter’s personal characteristics, as the investigator can unknowingly guide the subjects on how to behave, resulting in experimental bias. The participants’ behavior is affected when they have clues, though subtle, about the study’s purpose. Moreover, the experimenter’s personal attributes, such as accent, age, and gender, may affect how the study subjects will behave. These attributes can have an effect on the outcome of the research.
The third type is demand characteristics, which entail all the subtle clues of the experiment containing hints to the research’s purpose. They can make participants change their behaviors and affect the results of the experiment. Additionally, when they know what is expected of them, they will alter their behavior to conform to the anticipations. Therefore, demand characteristics can have an effect on the study’s results.
The third type is the participant or person variable because individual differences between participants, such as mood, concentration, anxiety, and intelligence, can affect the results of the study. For example, a participant performing a memory test when tired would lead to unreliable results, and the experimental design chosen can affect the outcomes of the experiment. Therefore, the participant or person variable can affect the results of the research.