TYPES OF EXPERIMENT & DESIGNS

• What is a lab experiment?


  Investigates relationships under controlled settings.

  Participants are aware they are in a study but may not know the true nature of the study.
• What is a field experiment?


  Where experiments are carried out in a natural setting.

  An independent variable is manipulated.
• What is a natural experiment? 


  These are in a natural setting with a naturally occuring DV and IV.

  -there is no manipulation of a variable - measuring the effect of something thats already happening.
• What is an experimental design? 


  Describes the way participants are allocated to experimental groups of an investigation.
• What are 3 strengths of a lab experiment?

  • High control leading to accuracy and objectivity
  • Individual behaviours can be isolated and tested.
  • Cause and effect - manipulate is the cause as the result of control.
• What are 2 weaknesses of a lab experiment?

  • Lacks ecological validity
  • Investigator effects and demand characteristics.
• What are 2 strengths of a field experiment?

  • ecological validity - real life setting
  • less demand characteristics.
• What are 3 weaknesses of a field experiment?

  • Ethical issues - no informed consent
  • Less control means they're difficult to replicate
  • Extraneous variables are difficult to control - unsure if the IV actually affects the DV.
• What is a quasi experiment?

  In these studies a researcher uses a naturally occurring IV.

  -They cannot randomly allocate participants to conditions.
• What is a repeated measures design?

  Where the same participants are allocated to all groups - take part in all conditions of an experiment.
• What are 2 strengths of repeated measures design?

  • The results will not be subject to participant variables - individual differences - putting more confidence in DV changes being solely due to manipulated changes in the IV.
  • Extra participants do not need to be recruited- saves money.
• What are 2 weaknesses of repeated measure design?

  • Risk of observing order effects (practice effects, or demand characteristics) - can be reduced by counterbalancing.
  • If a participant drops out, data will be lost from all conditions of the experiment rather than one.
• What is independent groups design?


  Where different participants take part in each experimental condition (they will be allocated randomly).
• What are 2 strengths of independent groups design?

  • Order effects cannot be observed, as no participants will be used in more than one condition. 
  • Data collection will be less time consuming if all conditions of the experiment are conducted simultaneously.
• What are 2 weaknesses of independent groups design?

  • Different participants need to be recruited for each condition, which can be difficult and expensive. 
  • There is a risk of participant variables (individual differences between participants) affecting the results between conditions, rather than solely manipulation of the IV.
• What method is used to control individual differences?

  Random allocation - it greatly decreases systematic error, so individual differences in responses or ability are far less likely to consistently affect results.
• What is matched pairs design?

  Where participants take part in only one experimental condition, but they are recruited specifically to be similar in relevant characteristics (e.g. intelligence, gender, age) to ‘match’ participants in the other condition(s).
• What are 2 strengths of matched pairs design?

  • Order effects will not be observed as participants only take part in one condition.
  • The participant matching process reduces the risk of participant variables (individual differences) from affecting results between conditions.
• What are 2 weaknesses of matched pairs design?

  • Different participants need to be recruited for each condition, which is difficult and expensive.
  • Matching is a complex process, and it will always be difficult to match participants identically.
• What is random allocation?

  It's a method to control individual differences, and is an extremely important process in research. In order to assess the effect of one variable on another, all variables other than the variable to be investigated need to be controlled.
• What is counterbalancing?

  A way of trying to control for order effects in a repeated measures design, e.g. half the participants do condition A followed by B and the other half do B followed by A.
• What is a strength of a natural / quasi experiment?

  • High ecological validity – due to the lack of involvement of the researcher, variables can be easily generalised to other/real life settings, resulting in high external validity.
• What is a weakness of a natural/quasi experiment?

  • Lack of control – natural experiments have no control over

  the environment and other extraneous variables, which means that the researcher cannot always accurately assess the effects of the

  IV - low internal validity.