Experimental Methods

• Lab experiments-

  Conducted in highly controlled settings where the researcher manipulates the IV, and records effects of the DV.

  There are no extraneous variables.
• Lab experiments are consider 'true' experiments
• Example:

  Peterson and Peterson

  Presented ppts with trigrams in 6 different conditions.

  Ppts recalled after 3,6,12,15 or 18 seconds.

  They found that memory decreased over time.

  3 seconds-> 80% memory

  18 seconds-> less than 10% of memory.
• Strengths-

  High control over extraneous variable meaning cause and effect can be established.

  Replication is possible due to high levels of control. Also means results can be checked for reliability.

  High internal validity.
• Weaknesses-

  Participants aware of being tested-possible demand characteristics.- Reduces validity.

  Artificial environment means it may lack generalisability.-Ecological validity low.

  Investigator effects may occur( unless double blind experiment.)
• Field experiment-

  Researcher manipulates the IV and records the effects of the DV but is conducted in a real-life setting.

  Anywhere behaviour occurs.
• Example:

  Piliavin arranged for a confederate to fall over on a New York subway.

  It tested who was more likely to help a man holding a walking stick and a man holding a bottle of whiskey( same man but dressed up in different costumes.)

  Man holding walking stick-> 95% of the time was helped.

  Man holding a whiskey bottle-> was 50% of the time helped.

  Women also stayed away from the man holding the whiskey bottle.
• Strengths-

  High Ecological Validity due to being conducted in a realistic setting.

  Behaviour is likely to be more valid and authentic- less demand characteristics.
• Weaknesses-

  Low control over extraneous variables, low internal validity and will be different depending on the experiment.

  Difficult to replicate them, they tend to be less controlled and less likely to be reliable.

  Possible ethical issues if unaware of being studied.
• Lab and Field is where is the study taking place etc the setting.
• Natural and Quasi is the IV which the researcher does not manipulate, and not considered true experiments.
• A natural experiment differs from other types of experiments in that it takes advantage of natural events or circumstances to create treatment and control groups, rather than artificially manipulating variables.
• A natural experiment is conducted in a natural setting where researchers have little if any control over the variables.
• Researcher takes advantage of a naturally occurring IV and effect it has on the DV.

  IV varies naturally.
• Example:

  The Winter War

  In 1939, Russia invaded Finland.

  Finland lost and many men died.

  Finnish women who were pregnant and lost their husbands due to this, their babies would turn out to be schizophrenic.
• Strengths-

  Provides opportunities for research that may not be otherwise conducted due to practical and ethical reasons.

  High external validity because they involve the study of real-life.
• Weaknesses-

  A naturally occurring event may happen, rarely limiting generalisation to other situations.

  Ppts may not be randomly allocated to conditions-bias.
• Quasi experiment-

  A quasi experiment takes a naturally occurring independent variable to see the effect on the dependent variable.
• In a quasi experiment researchers often take advantage of situations that are naturally occurring.
• Experiments are designed to study cause and effect.
• Independent variables in lab experiments are manipulated to see if there is any change or effect on the outcome of the results.
• IV is not something that varies at all- Simply between people that exist.

  EG: Experiment where the IV a variable such as age, gender, locus of control etc.
• Example:

  Psychologist wanted to see if ethnicity has an effect on personality types.

  Assigned 5 ppts to different groups based in ethnic backgrounds.

  Gave them all a personality test and compared the results.
• Strengths-

  Carried out under controlled conditions and share strengths of lab experiments.
• Weaknesses-

  Ppts are aware of being tested- possible demand characteristics.

  Ppts cannot be randomly allocated and therefore there may be confounding variables.