extraneous variables

• participant variables are extraneous variables that are personal characteristics of the participant such as age or intelligence.
• Investigator effects in a study can occur when the researcher influences the behaviour of the participants, which then affect the results of the study. This could be physical characteristics, accent or voice or the researcher being unconsciously biased. For example, female researchers may gain different results from a male one
• situational variables are anything external to the participants and the researcher that could affect the behaviour of participants such as room temperature and noise levels.
• demand characteristics are situational variables or investigator effects that act as hints which enable participants to guess aim of study.
• Some participants respond to demand characteristics and sometimes behave the opposite to the way they think the researcher wants them to behave or sometimes behave the way they think the researcher wants them to behave.
• extraneous variables are variables other than the IV that might affect the DV
• there are 3 main types of extraneous variables:

  • participant variables
  • situational variables
  • investigator effects
• confounding variables are uncontrolled extraneous variables that negatively affect results
• single-blind procedure is where participants have no idea which condition of the study they are in
• double-blind procedure is where neither participants or researchers know which conditions participants are in.
• the double blind procedure prevents investigators from unconsciously giving participants clues as to what conditions they are in and reduces demand characteristics
• Uncontrolled extraneous variables reduce the validity and the reliability of a study.
• Extraneous variables can be controlled through standardisation. This is when researchers make an extraneous variable the same for all participants, so that validity and reliability increase.
• Standardisation can be used to control investigator effects and situational variables.
• Participant variables can be controlled by matching. This is where the researcher makes sure a particular characteristic of the participants is divided equally across groups. However, limitations of matching are that it can be time-consuming because the researcher has to measure the personal characteristics of participants and then identify participants with similar characteristics and we can’t control for every possible participant variable that could affect the results of the study.
• Random allocation is when participants are assigned at random to different groups in order to ensure similar participants in each group.
• When participants don’t know what experimental group they’re in, they are blind to the experimental group making them less able to guess what the researcher is investigating.