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Mastering Experimental Control in Scientific Psychology

Learn essential techniques in scientific psychology to control experimentation variables effectively and ensure reliable research outcomes. Explore methods such as randomization, elimination, constancy, balancing, counterbalancing, and more for accurate results.

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Mastering Experimental Control in Scientific Psychology

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  1. The Science of Psychology

  2. Last week… • Science is a structured method of gaining new knowledge about the world • Scientific psychology has some unique problems: • Experimentation • Manipulate? • Measure?

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

  4. 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

  5. Experimental Control • Extraneous Variables • Experimenters • Physiological differences • Rosenthal effects

  6. Experimental Control • Extraneous Variables • Participants • Demand characteristics • Good participant effect • Response biases

  7. 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

  8. Basic Control Techniques • Elimination • Extraneous variables are completely removed from the experiment

  9. 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

  10. 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

  11. 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

  12. Participant 1 Participant 2 Participant 3 Participant 4 Participant 5 Participant 6 P C P C P C C P C P C P The Cola Wars!

  13. 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 The Cola Wars!

  14. 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

  15. 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

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