Ch13 Flashcards
Quasi-Experiments
researchers can’t necessarily randomly assign participants to the level of the IV (which also may be a quasi-IV)
types of quasi-experiments
- Independent groups quasi-experiments
- Repeated measures quasi-experiments
Non-equivalent control group design
an ind. group quasi-experiment design- at least one treatment group and one comparison group (separate participants) but they haven’t been randomly assigned
types of Non-equivalent control group design (ind groups)
- Non-equivalent control group posttest-only design
- Non-equivalent control group pretest/posttest design
Non-equivalent control group posttest-only design
(ind groups) not randomly assigned to groups, and tested only after exposure to one level of the IV or the other
Non-equivalent control group pretest/posttest design
(ind groups) not randomly assigned to groups, tested both before and after intervention
Repeated-Measures Quasi-experiments (+ what does it rely on)
- analogous to repeated measures designs in true experiments- all participants experience all levels of IV, IV not manipulated
- Relies on something already occurring, like an already scheduled event, new policy, etc (ex: food break and parole decisions)
types of repeated measure quasi-experiments
- Interrupted time series design
- Non-equivalent control group interrupted time series design
Interrupted time series design
- repeated measures quasi-experiment study that measures participants repeatedly on a DV before, during, and after an “interruption” caused by an event (ex:food break and parole decisions)
- Also can be in real experiments, with a manipulated IV
- In is one- measured ordinally (1st, 2nd, 3rd)
Non-equivalent control group interrupted time series design
combines interrupted times series (repeated measures) and non-equivalent control group (independent groups) designs- with no experimental control over either IV
Internal validity threats in quasi-experiments
- selection effects
- design confounds
- maturation effects
- regression to the mean
- attrition threats
- testing and instrumentation threats
- observer bias, demand characteristics, placebo effects
selection effects (how to help)
Unaccounted for differences between groups- only relevant to ind groups
- Matched groups can help
- Waitlist design- have half the group get surgery right away, half wait (true experiment)
design confounds ( + how to help)
Extraneous variables (vary systematically)
- Look into and rule out
maturation effect (+ help)
- pretest/posttest- an observed change could’ve emerged over time
- Comparison group
history threat (+ help)
External historical event happens to everyone at the same time
- Comparison group
- Selection-history threat if only applies to one group
regression to the mean (+ help)
Occurs when extreme finding caused by random factors, unlikely to happen again, gets less extreme over time
- pretest/posttest only, only if the initial score is extreme
- In experiments, random assignment prevents it
attrition threats (+help)
When people drop out systematically- pretest/posttest
- Missing values analysis- shows if drop-outs were systematic
Testing and instrumentation threats (+ help)
Occurs when measured more than once- if not measured the exact same way
- Testing threats- participants’ answers change b/c they’ve been tested before
- Comparison group
observer bias (observer bias, demand characteristics and placebo effect) + help
Human subjectivity
- experimenter’s expectations influence interpretation of results- both construct and internal validity threatened
- masked or double blind