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# Methods of experimental control - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about 'Methods of experimental control' - river

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Presentation Transcript

### Methods of experimental control

Randomization and Matching

Counterbalancing

Controlling participant and experimenter error

• 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

• 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.

• 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

• 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

• 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.

• 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

• Double-blind placebo model

• Disguise techniques

• Retrospective report, probes, and the think-aloud technique: Reactive effects caveat.

• Caution

• Blind techiques

• Automation