true experimental designs Flashcards
what is a true experimental design?
often referred to as ‘randomized-control trials (RCT’s)
follows these principles:
- random selection
- random assingment
- use of control group
- manipulation
what is the difference between random selection and random assignment?
random selection is the chance of being selected from a population.
random assignment is being assigned to groups
- everyone given equal opportunity to be part of any group (control, experimental groups)
control group
often recieves no treatment
- it is important to determine if an effect is present
experimental group
recieves treatment
in a simple model:
- 1 control and 1 treatment
(2x2 model)
in a complex model:
- 1 control and multiple treatments
what is the purpose of a pre-test?
it is important to determine that groups are equal before any intervention
- but, in RCT’s groups are randomly selected and randomly assigned
validity in experimental designs
validity is the treatment / test / intervention doing what it is intended to do
- an experiment needs to be valid to be viewed as relevant
internal vs external validity
internal validity:
- how much control we have in the experiment
- extraneous variables can impact results
external validity:
- how generalizable our results are
- need to consider threats and control them as much as possible
threats to internal validity
6
participant selection
practice effects
regression to the mean
instrumentation
mortality
maturation
threats to external validity
3
effect of the pretest
- has influence on how generalizable the results are
demand characteristics
experimenter effects
- white coat effect
- someone of influence in the room who could impact the results
how do we control threats?
- match groups based on similarities
- find similar groups
- control - use techniques that allow for controlling extraneous variables
