The Experimental Method

• Laboratory experiment

  Conducted under controlled conditions. Researcher manipulates the IV to measure the effect on the DV.

  Strengths: Highly controlled = minimises extraneous variables, clear cause and effect and standardised procedures (increases validity and reliability).

  Limitations: Potentially more demand characteristics displayed, low mundane realism and low ecological validity.
• Field experiments


  Carried out in natural conditions (anywhere that’s not a lab). Researcher manipulates IV to measure effect on DV. Pps don’t know they’re being observed.

  Strengths: Low chance of demand characteristics and higher ecological validity.

  Limitations: Ethical issues (e.g. lack of informed consent) and poor reliability (less control over extraneous variables, conditions can’t be replicated).
• Natural experiment


  Researcher does NOT manipulate the IV and instead examines the effect of an existing IV on the DV. IV is naturally occurring (e.g. a flood or earthquake). Behaviour of people affected is either compared to their own beforehand or with a control group who haven’t encountered the IV.

  Strengths: High ecological validity and less issues with demand characteristics.

  Limitations: Sample bias may occur (due to being unable to randomly allocate Pps to conditions) and ethical issues (e.g. lack of informed consent, deception, etc).
• Quasi experiments 


  Also contain a naturally occurring IV but one which already exists. IV is a difference between people (e.g. age, gender or a personality trait). Researcher examines the effect of IV on the DV. Don’t have to be conducted in a natural setting but often are. There’s no random allocation of Pps to conditions as the IV is pre-existing.

  Strengths: Less expensive and easy to compare since IV is pre-existing.

  Limitations: Can’t confidently infer cause and effect (there’s no direct manipulation of the IV and poor reliability (can’t easily be replicated due to lack of control).
• Directional hypothesis


  Predicts how something will change

  Example: Pps will learn a list of words significantly MORE quickly… Key words: higher, lower, more, less, increase, decrease, positive and negative.
• Non-directional hypothesis 


  Predicts something will change in the experiment.

  Example: There will be a significant difference…
• Null hypothesis


  There will be no significant difference…
• A hypothesis is a clear and precise prediction about the difference or relationship between the variable in the study.
• Extraneous variables are additional, unwanted variables that can affect the results of an experiment. They don’t confound the findings of the study, just make it harder to detect a result.

  Examples: age of Pps, lighting in the room, etc.
• Confounding variables change systematically with the IV and happen to be coincidental.

  Example: studying if energy drinks make people more talkative. The 1st group may have coincidentally just been more chatty then the 2nd group - adding an unintended additional IV (personality).
• Random Sampling


  Every member of the target population has an equal chance of being selected. Pps randomly selected from a list (e.g. names in a hat or random name generator)

  Strengths: No researcher bias and quick/ easier to acquire.

  Limitations: Can be unrepresentative of the population.