Experimental method

• aim

  a general expression of what the researcher intends to investigate
• hypothesis - a statement of what the researcher intends to investigate

  It should be operationalised, i.e. clearly defined and measurable.

  Directional hypothesis - states whether there will be a change or not or specifies an outcome.

  Non-directional hypothesis - doesn't state any specific outcome or relationship between the variables
• experimental method

  a researcher causes the IV to vary and records its effect of the IV on the DV. There are different levels of the IV.
• Extraneous and confounding variables

  • EVs - 'nuisance' variables that do not change with the IV. Some can be controlled by the researcher.
  • CVs - change systematically with the IV so we cannot be sure whether a change in the DV is due to them interfering or the IV.
• demand characteristics

  refers to any cue from the researcher or research situation that may reveal the aim of the study. this can lead to participants changing their behaviour which can reduce validity.
• investigator effects

  any effect of the investigator's behaviour on the outcome of the research (the DV)
• randomisation

  the use of chance when designing investigations to control for the effects of bias
• standardisation

  using exactly the same formalised procedures for all participants in a research study
• control groups

  used for the purpose of setting a comparison - they act as a 'baseline' and help to establish causation
• single blind and double blind studies

  Single blind - a participant doesn't know the aims of the study so that demand characteristics are reduced.

  Double blond - both participant and researcher don't know the aims of the study to reduce both demand characteristics and investigator effects
• independent groups - participants should be randomly allocated


  Pros:

  • no order effects
  • participants won't guess aim

  Cons:

  • participant variables (extraneous and confounding variables)
  • more participants
• repeated measures - order of conditions should be counterbalanced to avoid order effects.


  Pros:

  • participant variables (controls CVs)
  • fewer participants needed

  Cons:

  • order effects are a problem
  • participants may guess aims
• matched pairs - two separate groups but each participant is related to each other by being paired by participant variables (age, gender, etc.)


  Pros:

  • lack of participant variables
  • no order effects

  Cons:

  • matching cannot be perfect
  • more participants needed