Experimental Research

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Experimental research method
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Experimental method

• Experimental research is a comparison-between-
  groups.
• The experimenters are seeking to discover cause
  and effect relationships by changing something to
  see if the change causes a difference to another
  thing.
• They alter the independent variable (IV) to see
  if it causes a difference to a dependent
  variable (DV).

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• A Classic, experimental method involves assigning
  subjects at random to either an experimental
  group or a control group.
• The control group is compared with the
  experimental group to assess the effects of the
  experiment on the experimental group.

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Switching on the light

• The independent variable(IV) can be likened to a
  light switch and the dependent variable (DV) can
  be likened to a light bulb.
• An experiment compares the results of exposure of
  one (independent) variable upon another (the
  dependent variable).
• Switch on (the IV switch) and the (DV) bulb
  (metaphorically) illuminates the room.

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Advantages of experimental research methods

• The experiment is probably the best scientific
  method for attempting to find causal
  relationships.
• It allows us to locate the variables which
  control or cause a problem to occur.
• For some researchers such as those in the
  physical sciences the experiment has good
  internal validity because of the degree to which
  all extraneous variables are controlled.

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Aims of experimental research

• Establish cause and effect relationships.
• Then, like a switch we can turn the phenomena
  on and off.
• This is useful as the ability to switch things on
  or off means, a) we can be reasonably confident
  weve found variables that cause or impact on the
  problem significantly, and b) we can use that
  knowledge to control or adjust such phenomena.
• Such knowledge has advanced natural science and
  medicine as mentioned.

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Issues in any experimental research

• Internal validity--This is summed up in the
  following question -Does the experiment test what
  we say it tests?
• How sure can we be that the changes in the DV we
  measured were caused by the changes in the IV?
• Are all extraneous variables or confounding
  variables (ie one which changes as IV changes)
  controlled?

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• External validity means how strong are the
  generalizations we can make from this research
  (if any)?

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Threats to validity of experiments

• Internal validity threats
• History mediating event or factor between pre-
  and post-test alternative possible explanation
  of effects. History refers to events that occur
  between the DV measurements in a repeated
  measures design

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More threats to internal validity of experiments

• Maturation refers to systematic changes in
  participants physiology or psychology that occur
  over time during an experiment
• E.g. fatigue, boredom
• Testing The effect of taking a first test upon a
  second or subsequent test
• measuring the DV causes a change in the DV.
• If your attention is being explicitly measured,
  you may be more attentive than you would be
  otherwise

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Even more threats

• Instrumentation
• Instrumental bias or instrumental decay
• Changes in a measuring instrument that occur over
  time
• Behavioral observations most susceptible
• Observers may become more skilled or fatigued
•  refers to the experience and familiarity of the
  participant with test taking.

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Yet other threats

• Selection bias If we choose participants in such
  a way that our groups are not equal before the
  experiment, we cannot be certain that our IV
  caused any difference we observe after the
  experiment.
• Mortality/Attrition Loss of people from
  comparison groups ( they die, they move, they get
  new jobs etc).

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Threats to Internal Validity

• Diffusion or Imitation of Treatments- can occur
  if participants in one treatment group become
  familiar with the treatment of another group and
  copy that treatment.
• Carry-over effects
• Specific treatments cause changes in the next
  treatment(s) and alter the participants score
• NOTE caused by experiencing a SPECIFIC treatment

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• Carryover effects
• are challenging for within-subjects research
  designs, that is, when the same participants are
  exposed to all experimental treatments and
  results are compared across different treatments.
  These designs are useful, among other reasons,
  because they allow a near perfect match of
  subject characteristics as the researcher
  compares measurements of the same participant.
  However, as the same subjects are used in all
  experimental treatments, there is a possibility
  that a previous treatment can alter behaviour in
  a subsequent experimental treatment. This is
  known as a carryover effect.
• One type of carryover effect is a practice effect
  , where participants perform a task better in
  later conditions because they have had a chance
  to practice it.

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Threats to External Validity

• Generality across Response Measures
• E.g. Physiological versus behavioral measures of
  a phobia treatment can affect one but not the
  other

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Social science experimentsExamples

• Asch(1955)-Opinion social pressure
• Milgram (1964)-Obedience to authority
• Zimbardo(1974)-psychology of imprisonment

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