Experimental Methods

• Independent Variable


  variable that's manipulated or altered by experimenter to see its effect on the DV

  a change
• Dependent Variable


  measured result of the experiment (as a result of the change of IV)

  a measure
• Extraneous Variables


  any other variables that may have an effect on the DV

  any extraneous variables that aren't controlled can become confounding variables
• Confounding variables


  identified after the experiment is conducted

  serious - prevents us from being able to interpret our findings
• Control


  achieved when, other than the IV, all other variables are held constant so the change in the dependent variable can only be due to manipulation of the IV
• Randomisation


  ppts may be randomly allocated to different conditions of IV

  is to ensure that any extraneous variables linked to the ppt are as likely to affect one group as the other and will have little or no effect on the DV
• Standardisation


  means all ppts in an investigation have exactly the same experience.

  ensures that individual experience doesn't cause the ppts to engage with study differently
• Laboratory experiment


  involves a manipulated IV and a controlled/artificial environment

  Advantages:

  - reliable

  - more objective

  - establish cause + effect

  Disadvantages:

  - can't be applied to real world - low ecological validity

  - demand characteristics

  - evaluation apprehension
• Field experiment


  experimental investigations carried out in the natural environment of those being studied

  experimenter still manipulates the IV

  Advantages:

  - natural - might perform better - ecological validity

  - less demand characteristics

  - cause and effect

  Disadvantages:

  - less controlled - in natural environment

  - difficult to replicate

  - possible ethical issues
• Natural experiment


  IV is naturally occurring and environment is natural

  Advantages:

  - high ecological validity

  - less demand characteristics

  - investigates the effect of independent variables that would be unethical to manipulate

  Disadvantages:

  - difficult to replicate

  - difficult to establish cause + effect

  - lack of control

  - sample bias -> ppts aren't randomly allocated to groups
• Quasi experiment


  IV is naturally occurring but generally tested in a controlled setting

  Advantages:

  - can be replicated

  - IV isn't manipulated by experimenter

  Disadvantages:

  - difficult to establish cause + effect

  - possibly confounding variables as ppts can't be randomly allocated to different conditions