Experiment types

• What is a laboratory experiment?

  An experiment conducted under controlled conditions to measure how changes in the independent variable affect the dependent variable.
• How does a field experiment differ from a laboratory experiment?

  A field experiment is conducted outside of controlled settings in a real-world environment.
• What is a quasi-experiment?


  An experiment where participants cannot be randomly assigned to the independent variable.
• Validity in an experiment is whether a result from any kind of study is a genuine one; whether the data collected really represents people’s everyday behaviour
• Validity can be internal or external
• Internal validity involves whether the researcher tested what they truly intended to test
• High internal validity means the IV was truly tested on the DV
• Low internal validity means the EV was tested on the DV
• External validity involves the extent to which the research results can be generalised to other people and settings (low internal validity means there must be low external validity)
• External validity is split into ecological and population validity
• Ecological validity is how well the results can be generalised to other settings and locations
• Population validity is the extent to which the results can be generalised to other people, to measure this a large variety of people is used and opportunity sampling is avoided
• Factors that affect validity:

  -demand characteristics

  -researcher bias

  -researcher effect
• Demand characteristics are cues that tell participants the true aim of your study, these cues can subconsciously affect their behaviour
• You can reduce demand characteristics by:

  -only using participants in one condition of the study

  -used unrelated (filler) questions

  -deception can be used

  -single blind procedure could be used

  -double blind procedure could be used
• Researcher bias is when a researchers expectations affect a participants behaviour
• Researcher bias can be reduced by performing a double blind study
• Researcher effect is when the researcher does something that affects the participants performance
• Researcher effect can be direct or indirect
• Indirect researcher effects encourage reactions in participant. These can avoided by using a script or using a double blind trial
• Indirect researcher effects analyse the test results in a biased way or create study bias. These can be avoided by peer reviewing the studies
• An experiment is a research method which demonstrates causal relationships
• Strengths of laboratory experiments:

  -extraneous variables are decreased

  -no environmental changes

  -researcher has more control

  -easily replicated
• Weaknesses of laboratory experiments:

  -could be unsettling environment

  -low ecological validity

  -low validity because the participants are aware of the study

  -demand characteristics and researcher bias/effect are increased
• Strengths of field experiments:

  -less demand characteristics

  -higher ecological validity

  -some control of extraneous variables
• Weaknesses of field experiments:

  -increases extraneous variables

  -lack of informed consent and therefore no right to withdraw

  -less control of extraneous variables

  -harder to replicate as it’s often more expensive or time consuming
• Quasi experiments involve a naturally occurring IV and the DV is measured in either a lab or field
• Strengths of a quasi experiment:

  -high ecological validity

  -allows research where IV can’t be manipulated
• Weaknesses of quasi experiments:

  -lack of control over IV (can’t tell if IV causes DV)

  -less control of extraneous variables

  -may be difficult to replicate