Solving Problems Controlling Extraneous Variables

• The placebo effect is when a subject receives an inert (lacking an anticipated chemical or biological action) treatment and improves because of positive expectancies.
• Balancing controls extraneous physical variables by equally distributing their effects across treatment conditions.
• Context variables are extraneous variables produced by experimental procedures created by the research setting environment, like assignment of participants to conditions.
• Single-blind experiments only control demand characteristics, since subjects are blinded to their condition.
• Precautions when setting good experiments:

  • Eliminate extraneous variables whenever possible.
  • Keep conditions constant where elimination is not possible.
  • Balance the effects of extraneous variables when constancy of conditions is not possible.
  • Be sure to assign individual subjects to treatment conditions at random.
• Physical variables are aspects of the testing situation that need to be controlled
• If you do not select your subjects randomly, your sample will be biased, resulting in less generalizability
• Social variables are aspects of the relationships between subjects and experimenters that can influence experimental results.
• The Rosenthal effect is the phenomenon in which experimenters treat subjects differently based on their expectations and their resulting actions influence subject performance.
• Elimination completely removes extraneous physical variables from the experimental situation (e.g., soundproofing a room).
• When there is a single experimenter, minimize face-to-face contact and closely follow the script.
• Demand characteristics are cues within the experimental situation that demand or elicit specific participant responses.
• How might an experimenter's personality affect experimental results?

  • Research on experimenter personality shows that when experimenters are warm and friendly, subjects learn more, talk more, earn better test scores, and are eager to please.
  • Hostile or authoritarian experimenters obtain inferior subject performance.
• A cover story is a false plausible explanation of the experimental procedures to disguise the research hypothesis from the subjects.
• Constancy of conditions controls extraneous physical variables by keeping all aspects of the treatment conditions identical, except for the independent variable.
• In a single-blind experiment, subjects are not told their treatment condition.
• 2 kinds of context variables: (1) those that occur when subjects select their own experiments; (2) those produced when experimenters select their own subjects.
• Selecting your friends might bias your sample, threatening external validity.
• Double-blind experiments control both demand characteristics and experimenter bias, since both the experimenter and subjects are blinded.
• The more extraneous variables we control, the more we increase internal validity, particularly when we control variables that can change along with the IV.
• Experimenter bias is any behavior by the experimenter that can confound the experiment.
• How can experimenters control personality variables?

  • Employ multiple experimenters to run an equal number of subjects in each of the experimental conditions (balancing).
  • Treat “experimenter” as an independent variable in statistical analysis. If an interaction is found, then the experiment was confounded.
• Because subjects do not know what to expect, changes in their behavior are more likely be caused by the IV.

  placebo effect
• This include subject recruitment, selection and assignment procedures, which may be controlled with some forethought.

  Context variables
• Removal of extraneous physical variables prevents them from operating differently across different treatment conditions.

  Elimination
• This is also called the Pygmalion effect and self-fulfilling prophecy

  Rosenthal effect
• These include demand characteristics and experimenter bias.

  Social variables
• Both you and your friends might act differently in your experiment than strangers.
• Effects of Demand characteristics:

  • They may lead participants to form hypotheses— either correct or incorrect— about the nature of the experiment.
  • Some participants may react in a compliant way to “help” the experimenter’s efforts, whereas others may react in a defiant way to “hinder” the experimenter’s efforts.
  • Other participants may simply perform in a way they think is expected of them.
• How can experimenters control personality variables?

  Videotape sessions to confirm consistent performance.
• When subjects are not told their treatment condition, this eliminates cues that might alter their behavior.

  single-blind experiment
• The variables may be controlled with the use of single- and double-blind experiments.

  Social variables
• The Rosenthal effect can confound an experiment, producing results consistent with the experimenter’s expectations.
• These may be addressed using control techniques so that the chances of an internally valid experiment can be attained.

  Physical variables
• They should be used sparingly, since they are a form of deception

  cover story
• In a well-constructed experiment, the IV not the extraneous variables, caused the effects – the experiment is high in internal validity. By also controlling the extraneous variables, we may be reducing external validity.
• Whatever the case, demand characteristics can affect the quality of the experiment.
• In Physical variables, the techniques include: elimination, constancy of conditions and balancing.
• Control for this possible threat by constructing procedures for acquiring subjects as carefully as you plan your experimental procedures.