Extraneous Variables

• Demand Characteristics


  These are aspects of the study that may be interpreted by participants as revealing the aim of the study and form expectations about how they should behave
• Investigator effects


  When the researcher influences the behaviour of the participants and therefore the results of the study
• Technique to Overcome demand characteristics


  • Single blind study
  • This means that the participant doesn’t know which experimental group they are in
• Advantage of single blind study

  There is less chance participants will respond to demand characteristics because they are less able to guess what the researcher is investigating
• Overcoming investigator effects


  using a double blind study which is when both the participant and the researcher are blind to the experimental group
• Advantage of double blind study

  Advantage of double blind study is that the researcher won't be able to form expectations about how the participants will behave so can control investigator effects and demand characteristics
• What are participant variables

  Extraneous variables that are personal characteristics of the participant which may affect the dependent variable
• What are situational variables

  Extraneous variables that are features of the external environment that could affect the behaviour of the participants
• What types of situational variables are demand characteristics?

  Situational variables that act as hints that enable participants to guess the aim of the study
• What are uncontrolled extraneous variables

  variables that reduce both the validity and reliability of a study
• What is standardisation


  a way of controlling extraneous variables by the researcher making an extraneous variable the same for all participants, so that validity and reliability increase
• We can use standardisation to control....

  • Situational variables
  • Investigator effects
• What is matching?


  making sure a particular characteristic of the participants is divided equally across groups
• Limitations: using matching to control participant variables

  •  It’s time-consuming because the researcher has to measure personal characteristics of the participants and identify participants with similar characteristics
  •  It’s impossible to control for every possible participant variable, so some participant variables may still affect the dependent variable
• What is random allocation


  Participants are assigned at random to experimental groups in order to ensure similar participants in each group and that participant variables are distributed evenly