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Lecture 17

Lecture 17 - Single Participant Experiments.docx

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Western University
Psychology 2800E
Doug Hazlewood

Single Participant Experiments (Or “small­n” experiments) Part 1: Reasons for using single­participant experiments 1. Group experiments tell us about “groups” of people, not individuals 2. Group scores (means) can misrepresent the behaviour of specific individuals 3. Group scores can misrepresent the behaviour of all individuals in the group - See W&M p. 297-298 o Fig 12.1: gradual learning at group level o Fig 12.2: sudden learning at individual level Note 1: Sometimes single participants are studied - But study can be replicated with other participants (to see if the results “generalize”) o So, also called “small-n” experiments o Each replication (with single P) is a separate experiment (look for “converging” pattern) Note 2: Has a long history in psychology - Pavlov’s studies of “classical conditioning” o Studied one dog at a time – then replicated in additional dogs; findings were generalizable; all dogs had the same effect - Skinner’s studies of “operant conditioning” o Didn’t discover operant conditioning through groups of rats and averaging their responses together – studied one rat at a time! Note 3: Also relevant to previous discussion: - Nomothetic research (what’s common in groups of people; do “group” experiments), - Ideographic research (what’s unique about each individual; do single-participant experiments) Note 4: They are experiments (have IV, DV, control all other variables) - Similar to within-group experiments (raise special problems with control and internal validity) Part 2: Comparison and Reversal Designs A. The Comparison (“AB”) design - Allows us to compare 2 conditions - A = no treatment (provides baseline measure when no treatment is present) - B = introduce treatment; measure effect o Compare A with B to see if treatment was effective - Nothing more than a pre-test post-test design, except only one participant - Example: o A = bar pressing during baseline o B = introduce reward [treatment] each time bar is pressed o If bar pressing increases after reward is introduced, does this mean that reward caused a change in behaviour? - Note: same as pretest-treatment-posttest design o Introduces possible confounds! Other “causes” that threaten “internal validity” - Example: o Rat got bored, bar became most interesting thing at exactly the same time that reward was introduced (if so, boredom and reward are confounded) o Only plausible if confound was introduced at exactly the same time as the treatment. Test this with… B. ABA “reversal” (or “withdrawal”) design - A = baseline (no treatment) - B = introduce treatment - A = withdraw treatment (what does this do?) o If behaviour goes back to baseline level, then it suggests the treatment had a real effect (e.g., rat stops pressing bar when reward is removed)  But maybe rat got bored with bar at exactly the same time that reward was removed (another confound)  If so… C. ABAB (“repeating treatments”) design - Reintroduce the treatment after ABA; if behaviour is influenced, treatment was effective o Or “ABABAB” design, etc. - If establish a unique co-variation between treatment and behaviour (behaviour occurs when treatment is present, doesn’t occur when treatment is absent) then we can say that treatment causes behaviour - Note: Not always possibleto reverse the effects of a treatment. E.g., o Learned skills are retained after treatment is removed (e.g., new reading program); o Unethical to remove a treatment that appears to be effective (e.g., new cancer drug). - BU
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