Types of experiments

• The three types of experiments

  Natural

  Laboratory

  Field
• A lab experiment takes place in a controlled environment where participants are typically tested one at a time
• Evaluate lab experiments


  • Advantage : controlling environment limits extraneous variables
  • Disadvantage : Lacks external validity
• A field experiment is a controlled experiment in which the IV is manipulated in a natural setting.
• Evaluate field experiments


  • Advantage : natural behaviour as participants tend to feel more comfortable
  • Disadvantage : Harder to control extraneous variables
• A natural experiment is when the IV is not manipulated by the researcher, but is naturally occurring
• Evaluate natural experiments


  • Advantage : no ethical issues
  • Disadvantage : bias, researchers did not allocate groups randomly
• Independent groups design


  Participants take part in only one condition
• Matched Participants design


  Researchers pair up participants in sample based on similarity
• Evaluate matched participants design

  • Disadvantage : time consuming
  • Advantage : Reduces participant variable, no order effects
• Evaluate independent group design


  Affected by participant variables
• Order effects meaning


  The orders in which participants do conditions can affect outcome of experiments
• Sampling


  Find sample of participants after experiment approval from BPS
• Target population


  Group in society which participants need to be drawn
• Gaining a sample 


  Smaller group of target population
• Sampling techniques


  • Opportunity sampling
  • Random sampling
  • Systematic sampling
  • Stratified sampling
• Opportunity sampling


  When researchers find participants who are easy to obtain

  Ex: elderly in a care home
• Evaluate opportunity sampling

  Convenient and quick

  Biased sample as doesn't represent target population
• Random sampling


  Randomised selection by numbers
• Evaluate random sampling


  Less biased

  Time consuming
• Systematic sampling


  Selecting participants in a regular way

  Ex: Every hundredth person
• Evaluate systematic sampling


  Reduces bias

  If groups were ordered in a biased manner, sample will also become biased
• Stratified sampling


  By determining size of particular groups in target population, sample will be selected in same proportions
• Evaluate stratified sampling


  Same percentage of groups in sample as in target population

  If researcher did not include certain characteristics, sample may be biased too
• Most researchers choose opportunity sampling because it is easy to implement and it is cheap.