PSY2 – Research Methods: Lesson 10

Extraneous Variables cont. (Controlling)

PSY2 RM PowerpointTeachers or students who want the original PPT please tweet @psychopepper

Learning Objectives

  • To KNOW and UNDERSTAND what the definition of a confounding variable is.
  • To KNOW and UNDERSTAND what investigator effects are.
  • To KNOW and UNDERSTAND what the various ways of controlling extraneous variables are.
  • To ANALYSE how researchers might accomplish the various ways of controlling extraneous variables.

Lesson Outline:


  1. Take notes on the definition of expectancy bias in booklet.
  2. To read the definition of confounding variables in booklet and discuss how extraneous variables and confounding variables are different. What does vary systematically actually mean!
  3. Take notes on the ways in which we control for extraneous variables in booklet and feedback ideas to the class.

Content Recap:

Extraneous Variables: Extraneous variables are nuisance variables which can bias the research and do not vary systematically with the IV. They are things which we are (largely) able to identify before we conduct our experiment and put measures in place to reduce or eliminate. If not they can seriously impact the internal validity of a study. They can confound the results because the change in the dependant variable (DV) may be due to the extraneous variables rather than the independent variable (IV).

Investigator Effects: When conducting research the investigator may bias the final outcome of the study in a number of ways. Mostly researchers are unaware that this is occurring, very occasionally however there is deliberate bias caused.

Expectancy Bias: A form of investigator effect whereby the investigator accidentally changes their behaviour based on their expectations of what should occur. For example watching a group more closely if they expect them to behave in a certain way.

Confounding Variable: Confounding variables do vary systematically with the IV. Another way this is sometimes described is a variable which changes/correlates with both the IV and the DV. for example with age comes experience. So when I change someone’s age for the purpose of an experiment, their experience also changes.

Pilot Study: A small scale version of the study conducted to check the procedure works and identify any extraneous variables. For example ensuring participants have enough time to complete the test.

Standardisation: Ensuring that all elements of the procedure are identical for all participants, for example writing instructions down and getting participants to read them to ensure each one got exactly the same experience.

Single Blind: Making participants unaware of what the test is about or what condition they are in.

Double Blind: Not only making participants unaware of what the test is about or what condition they are in but also using a naive researcher to conduct the test who also does not know.

Randomisation: Where ever possible randomising elements of the procedure. For example, randomly allocating participants to which condition or randomising the presentation of the questions or test items.

If you would like to access PsychoPepper’s Glossary of Terms please click here

Study Notes (TBC):

If you would like to download a set of study notes for this lesson, you can do so here. If you would like access to the original word file please tweet @psychopepper


I would suggest that you have a copy of one of the textbooks which will allow you to read around the subject matter, pre-read ahead of lessons or even take extra notes/practise questions afterwards. I would recommend the following (you do not need to replicate books, one of each type is plenty!)

Extra ReadingElephants on Acid or Hippo Eats Dwarf

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