Extraneous/cofounding variables and demand characteristics

• Levels of the IV

  • In order to test the effect of the IV we need different experimental conditions. 
  • We need a comparison:
  • Compare two groups of participants - those who drink SpeedUpp with those who drink water
  • In either case the two conditions are no SpeedUpp or drinking SpeedUpp.
  • These are the two levels of the IV. 
  • The control condition (no SpeedUpp / drink of water) and the experimental condition (energy drink).
  • The directional hypothesis to reflect this could be:

  The group that drinks an energy drink will be chattier than the group that drinks water.
• Operationalisation of variables

  • Defining variables clearly in terms of how they can be measured.
  • Many of the things that psychologists are interested in are often a little fuzzy and not easy to define.
  • We need to ensure that the variables being investigated are as unfuzzy and measurable as possible
  • So, a much better hypothesis than the one above would be:

  After drinking 300 ml of SpeedUpp, participants say more words in the next five minutes than participants who drink 300 ml of water.
• Research Issues

  There will always be a number of unwanted factors that can potentially affect the relationship between the independent and dependent variables, spoiling or distorting the results in the process.

  Fortunately, psychologists are aware of this issue and have devised several different ways of tackling it.
• Extraneous Variables

  • The key to an experiment is that an IV is manipulated to see how this affects the DV. Any other variable that might interfere with the IV or DV are unwanted variables are called extraneous variables 
  • Where possible, are identified at the start of the study and then steps  are taken to minimise their influence.
  • Examples:
  • Age of participants trying the drink
  • Lighting of the lab as participants try our energy drink
• What are confounding variables?

  Variables that change systematically with the IV
• How do confounding variables affect research results?

  They can obscure the true effect of the IV
• In the energy drink study, how many participants were used for the Speedupp condition?

  Twenty participants
• Why were the first ten participants in the Speedupp condition particularly excited?

  They saw Prince William in the hallway
• What unintended variable was introduced in the energy drink study?

  Excitement level of the participants
• What is participant reactivity in experiments?

  Participants try to make sense of the situation
• What was the effect of the excitement on the Speedupp group's behavior?

  They were found to be chattier
• Why is participant reactivity considered a significant extraneous variable?

  It is difficult to control in experiments
• What are demand characteristics in an experimental situation?

  Clues that help participants interpret the study
• Why can't researchers be sure about the cause of the Speedupp group's behavior?

  Because excitement may have influenced results
• How might participants use demand characteristics during an experiment?

  To second-guess the experimenter's intentions
• What is the relationship between confounding variables and independent variables (IV)?

  • Confounding variables change systematically with the IV
  • They can obscure the true effect of the IV
  • They introduce uncertainty in research findings
• What behavior might participants exhibit due to demand characteristics?

  They may over-perform or under-perform
• What are the implications of having confounding variables in an experiment?

  • Results may be misleading
  • Difficulty in establishing cause-and-effect relationships
  • Need for careful experimental design to control variables
• How can participants' behavior affect the dependent variable (DV) in a study?

  It may no longer be natural due to reactivity
• What is the main consequence of participant behavior being affected by demand characteristics?

  It introduces an extraneous variable
• What is the impact of participants trying to please the experimenter?

  They may over-perform in the study
• What might happen if participants deliberately under-perform?

  They may sabotage the results of the study
• What is participant reactivity related to in research?

  Investigator effects
• How might investigator effects manifest in a study?

  Through unintentional researcher behaviors
• In the energy drink study, what behavior might indicate an investigator effect?

  Smiling more with certain participants
• Randomisation

  • There are simple steps that a researcher can take to minimise the effect of extraneous/confounding variables including ‘randomisation’.
  • Refers to the use of chance methods to reduce the researcher's unconscious biases when designing a study (attempt to control investigator effects).
  • A memory experiment involving participants recalling words from a list. The order of the list should be randomly generated so the position of each word is not decided by the researcher.
• What does the term "investigator effect" refer to?

  Unwanted influence of the investigator on outcomes
• Who suggested the broader definition of investigator effects in 2006?

  Hugh Coolican
• What additional actions of the researcher might be considered as investigator effects?

  Selection of participants and study materials
• How can the design of a study influence investigator effects?

  Through participant selection and instructions
• Standardisation

  • All participants should be subject to the same environment, information and experience.
  • To ensure this, procedures are standardised, there is a list of exactly what will be done in the study. This includes standardised instructions that are read to each participant. 
  • Such standardisation means that non-standardised changes in procedure do not act as extraneous variables.