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Methods of experimental control. Randomization and Matching Counterbalancing Controlling participant and experimenter error. Randomization. Random selection: a representative sample Basis of generalizability or external validity Exhaustive sampling is good, but difficult

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methods of experimental control

Methods of experimental control

Randomization and Matching

Counterbalancing

Controlling participant and experimenter error

randomization
Randomization
  • Random selection: a representative sample
    • Basis of generalizability or external validity
    • Exhaustive sampling is good, but difficult
  • Random assignment: equivalent groups
    • Basis of controlling most evars
    • Chance of nonequivalent groups covered in error term of statistical analysis
  • Random sequencing: order effects
matching
Matching
  • Since randomization assigns individual differences to the error term, it has one unfortunate effect: reducing power.
  • Matching techniques increase group equivalence, so it increases power
  • Matching must be complemented with random assignment to produce randomized blocks designs or matched groups designs.
matching tactics
Matching tactics
  • Hold extraneous variable constant
    • Limits population size
    • Limits generality of results
  • Manipulate extraneous variable in design
    • Beware whynot variables
  • Use a yoked control design
  • Equate participants: Precision control
  • Equate participants: Frequency distribution
counterbalancing
Counterbalancing
  • Sequencing effects:
    • Order effect
    • Carry-over effect
  • Counterbalancing tactics
    • Intrasubject for repeated measures: ABBA
    • Intrasubject/intragroup: ABBA/BAAB
    • Intragroup
    • Incomplete: Latin and Greco-Latin squares
latin squares
Latin Squares
  • In Latin Square counterbalancing, each different treatment is symbolized by a letter, different applications of treatments are in columns, and different occasions are in rows.
  • The number of rows and columns equals the number of treatments.
  • Each treatment letter appears once and only once in each row and in each column.
latin squares7
Latin squares
  • A B C A B C D A B C D
  • B C A B C D A B D A C
  • C A B C D A B C A D B
  • D A B C D C B A
controlling experimenter and participant effects
Controlling experimenter and participant effects
  • Double-blind placebo model
  • Disguise techniques
  • Retrospective report, probes, and the think-aloud technique: Reactive effects caveat.
  • Caution
  • Blind techiques
  • Automation