Experiment type

What is a laboratory experiment?

An experiment that takes place in a controlled environment where the experimenter:

• Manipulates the IV

• Measures the DV

What are standardised instructions?

The instructions given to each participant are kept identical to:

• Help prevent experimenter bias

What are standardised procedures?

All participants are treated exactly the same at every step of the research, so they all have the same experience.

What are control and experimental groups?

• Control group: Treated normally, provides a baseline measure of behaviour without the experimental treatment

• Experimental group: Receives the experimental treatment

• Experiments always have at least one experimental group

What are the strengths of laboratory experiments?

• Easy to replicate due to standardised procedures

• Allow precise control of extraneous and independent variables

• Enable establishment of cause and effect relationships

What are the weaknesses of laboratory experiments?

• Artificial setting may produce unnatural behaviour

• Leads to low ecological validity → cannot generalise to real life

• Demand characteristics and experimenter effects may bias results and become confounding variables

What is a field experiment?

An experiment that takes place in a natural setting where the experimenter:

• Manipulates the IV

• Measures the DV

What are the strengths of field experiments?

• Behaviour is more realistic due to natural setting

• Higher ecological validity than lab experiments

• Less demand characteristics, especially if covert

What are the weaknesses of field experiments?

• Less control over extraneous variables

• Results may be biased

• Difficult to replicate exactly

What is a natural experiment?

Conducted in a real-life environment where:

• The experimenter does NOT control the IV

• The IV occurs naturally

What are the strengths of natural experiments?

• Very high ecological validity

• Behaviour reflects real life

• Less demand characteristics

• Can be used when it is ethically unacceptable to manipulate the IV (e.g. stress research)

What are the weaknesses of natural experiments?

• May be expensive and time-consuming

• No control over extraneous variables

• Difficult to replicate exactly

What is a quasi experiment?

An experiment where the IV:

• Cannot be manipulated or randomly assigned

• Is naturally occurring within participants (e.g. male/female, young/old)

What are the strengths of quasi experiments?

• IV is naturally occurring, so may be more reflective of the individual

• Allows study of variables that would be unethical to manipulate

What are the weaknesses of quasi experiments?

• Difficult to control extraneous variables

• Cannot be sure IV caused the effect on the DV

• Hard to replicate

• May lack internal and external reliability

How do the different experiments compare in control and validity?

• Lab experiment: High control, low ecological validity

• Field experiment: Moderate control, higher ecological validity

• Natural experiment: Very low control, very high ecological validity

• Quasi experiment: Low control, IV cannot be manipulated

What is the difference between field, natural, and quasi experiments?

• Field experiment:
  Takes place in a natural setting where the researcher manipulates (controls) the IV.

• Natural experiment:
  Takes place in a real-life setting where the IV is not controlled and is based on an external event that has occurred to participants.

• Quasi experiment:
  The IV is not controlled and is pre-existing within participants (e.g. age, gender).