The Science of Psychology

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The Science of Psychology
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Last week

• Science is a structured method of gaining new
  knowledge about the world
• Scientific psychology has some unique problems
• Experimentation
• Manipulate?
• Measure?

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Experimental Control

• Extraneous Variables
• Nuisance variables
• Make the effects of the IV more difficult to
  determine
• Participant characteristics
• Unintended influences of experimental situation

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Experimental Control

• Extraneous Variables
• Confounding variables
• Influence the difference between groups
• The differences observed between groups could be
  attributed to the IV or the confound

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Experimental Control

• Extraneous Variables
• Experimenters
• Physiological differences
• Rosenthal effects

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Experimental Control

• Extraneous Variables
• Participants
• Demand characteristics
• Good participant effect
• Response biases

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Basic Control Techniques

• Randomization
• Individuals have an equal chance of being
  assigned to any group in the experiment
• Allows us to assume groups are roughly equivalent
  before administering the IV

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Basic Control Techniques

• Elimination
• Extraneous variables are completely removed from
  the experiment

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Basic Control Techniques

• Constancy
• An extraneous variable is reduced to a single
  value experienced by all participants
• Standard control technique
• Hold environment, temperature, lighting constant

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Basic Control Techniques

• Balancing and Counterbalancing
• Balancing
• Achieves group equality by distributing
  extraneous variables to all groups
• Counterbalancing
• Controls order effects by presenting treatments
  in a different sequence
• Order or sequence effects
• Carryover effects
• Differential carryover

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Basic Control Techniques

• Within-Subject Counterbalancing
• Within-Group Counterbalancing
• Each treatment must be presented to each
  participant an equal number of times
• Each treatment must occur an equal number of
  times at each testing session
• Each treatment must precede and follow each of
  the other treatments an equal number of times

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The Cola Wars!

• Participant 1
• Participant 2
• Participant 3
• Participant 4
• Participant 5
• Participant 6

• P C
• P C
• P C
• C P
• C P
• C P

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The Cola Wars!

• Participant 1
• Participant 2
• Participant 3
• Participant 4
• Participant 5
• Participant 6

• P C DP
• P DP C
• C P DP
• C DP P
• DP P C
• DP C P

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Basic Control Techniques

• Single- and Double-Blind Experiments
• The experimenter (single-blind) or both the
  experimenter and participants (double-blind) are
  unaware of the participants condition

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Basic Control Techniques

• Altering response sets
• Rewrite survey items so that some negative
  responses indicate agreement and some positive
  responses indicate disagreement
• Check for socially desirable responses in your
  survey and/or potentially undesirable cues