Experiments and quasi-experiments

ROXOA
R=Randomization
O=Observation
X=Treatment
A=Analyze data

Experiments:
ROXOA
RO OA

R XOA
R OA

Threats to validity: R

Selection (messed up the random assignment)
Mortality (participants drop out of groups unequally) If most of the females drop out in one group, it throws off the experiments. Called mortality because it references the use of rats and rats dying at unequal rates.

Threats to validity: O

Testing: the testing sensitizes participants to treatment
Instrument: measurement devices are messed up)

Threats to validity: X

Experimenter bias (treat groups unequally)
Experiment diffusion (something contaminates the control group)

Threats to validity: O - O (multiple observations)

History (something affects participants outside of the experiement like TV show, breaking news, etc.)
Maturation (something within the participants changes)

Threats to validity: A

Statistical regression (extreme scores are not repeatable, tend to move toward the mean in second observations)
Statistical conclusion (improper or faulty analysis)


Quasi-experiments

Do not include randomization, so groups are not equivalent.

1. Nonequivalent control group: OXOA compared with O_OA
2. Simple interrupted time-series: OOOOOXOOOOOA (no random and no group compare)
3. Combined (Time series with nonequivalent control group): OOOXOOOA compared with OOO_OOOA.