extraneous variables

• 3 types of extraneous variables

  1. participant
  2. situational
  3. investigator
• what are participant variables?


  personal characteristics of participant variables that may affect DV
• what are investigator effects?

  the researchers influences the behaviour of participants and therefore results of study
• what are situational variables?

  extraneous variables that are a feature of external environment
• what are demand characteristics?

  Situational variables and investigator effects that act as hints that enable participants to guess the aim of study.
• what is standardisation?

  making the extraneous variable the same for all participants so that validity and reliability increase
• which extraneous variables can we standardise?

  participant variable

  investigator effects
• what does matching mean?

  making sure a particular trait/charcteristic of participants is divided evenly across groups
• Limitations of Matching:

  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.
• random allocation

  Participants are assigned at random to different groups in order to ensure similar participants in each group.
• to control situational effects and investigator effects you use...

  standadisation
• single blinding is used to reduce...

  demand characteristics
• double blinding is used to reduce...

  demand characteristics and investigator effects