Research Methods
Lesson 3
Introduction to Extraneous Variables Investigation & Design Produced by
Extraneous Variables
Situational Variables
Participant Variables
Demand Characteristics
Investigator Effects
Definition: • An extraneous variable (EV) can be defined as being any variable other than the independent variable that might affect the dependent variable (DV). • The effect found between two groups in an investigation can be due to an extraneous variable (EV) opposed to the independent variable’s (IV) manipulation. If this does happen we have poor controls and all other variables in an experiment were not controlled for or kept constant. • If there is evidence of an extraneous variable having an effect on your investigation we say that these extraneous variables (EV) are confounding variables.
Introduction to extraneous variables (EV): • In research we need to control all extraneous variables (EV) otherwise we cannot be sure that it is the independent variable that has affected the dependent variable (DV). Hypothetical situation: • We want to investigate whether a healthy school breakfast helps improve performance in class tests. •
We manage to recruit two identical groups. They are of the same age, have similar mental ability and intelligence and participants study AS Psychology.
• One group has a healthy breakfast for a week and the other does not. The have exactly the same lessons and so on. Just say hypothetically we have thought about all extraneous variables and controlled for them.
The investigation: • Our investigation will involve giving both groups the same identical test in a very similar environment. • Just say we use the psychology classroom for that purpose. However, because we have two large groups we give the group that has a healthy breakfast the test in the morning and the other group takes the exact same test in the same classroom but in the afternoon. The results: • After our analysis of the data the results suggest that the group that had a healthy breakfast and took the test in the morning performed better in the class test. So we want to conclude from our investigation that a healthy breakfast does help improve performance in class tests.
Conclusion: • This is not true. The effect we found (that is the DV) is not necessarily due to the manipulation of the independent variable. In the case above the IV would be breakfast and we manipulate it by giving one group a healthy breakfast and the other group just an average greasy breakfast whilst we controlled all other variables. • The question is did we control all variables? The answer is no, as one group took a test in the morning and the other group took the test in the afternoon. • The results found could be due to the time of day the students took the test opposed to the breakfast which we believe. Some students could have been disadvantaged in the afternoon as they may have been experiencing fatigue. Therefore we have an extraneous variable which is time of day that is confounding.
Types of extraneous variables: • There are a number of different types of extraneous variables that can be confounding which psychologists need to take into account when implementing and designing their investigation. Situational variables: • These are variables connected with the research situation. For example, room temperature, instructions, time of day, lighting and materials used in an investigation. • Situational variables are controlled by standardisation. By this we mean ensuring that the only variable that varies between the two groups or conditions is the IV.
Participant variables: • These are variables connected with the research participants. For example, intelligence, age, gender, and personality. • Participant variables are controlled by appropriate sampling and selection methods sometimes referred to as participant or experimental design. • For example, if we are carrying out an investigation on memory ability, we need to make sure that participants in one group are evenly matched to participants in the other. • Randomly assigning participants to the two conditions also helps to control participant variables by reducing any bias.
Demand characteristics: • The demand characteristics in an experiment are those things that encourage or invite the participants to behave in a certain way. These things are cues in the external environment that lead participants to think they ought to behave or act in a particular fashion. • Demand characteristics can be defined as cues in the environment that help the participant work out what the hypothesis is. This can lead to social desirability effects where the participant behaves in a way that the hypothesis will be supported or the ‘screw you’ effect where the participant deliberately disrupts the research.
Investigator effects: • Investigator effects are those aspects of the researcher’s or investigator’s appearance or behaviour that can lead a participant to believe that they need to act in a particular way. • Investigator effects can be defined as the conscious or unconscious appearance or behaviour that can lead a participant to believe that they need to act in a particular way, thus leading self-fulfilling prophecy.
Controls for demand characteristics and investigator effects: • These two threats to the internal validity of the investigation or research can be controlled using the following techniques: Demand characteristics – single blind technique: •
Adopting a single blind technique, a procedure in an experiment where the participants do not know the hypothesis and do not know which condition they are in.
Investigator effects – double blind technique: • Adopting a double blind technique, a procedure in an experiment where neither the participants nor the research assistant know the hypothesis or the conditions the participants are in. This will involve a research assistant carrying out the data collection on behalf of the experimenter.
Further Reading: • www.psychologyrevise.com Investigation and Design Variables.
Research Methods Extraneous
• Wider reading – more practical examples on extraneous variables. • Mind Map