Experimental Design

1. *EXPERIMENTALEXPERIMENTAL
DESIGNDESIGN*
General Structure of theGeneral Structure of the
Experiment not itsExperiment not its
specific content ,designspecific content ,design
is made up of numbersis made up of numbers
of treatments.of treatments.

2. DETERMINING OFDETERMINING OF
DESIGNDESIGN
1.1. Number of independentNumber of independent
variablesvariables
2.2. Number of treatment conditionsNumber of treatment conditions
neededneeded to make a fair test.to make a fair test.
3.3. Whether the same or differentWhether the same or different
subjects are used in each of thesubjects are used in each of the
treatment conditions.treatment conditions.

3. BETWEEN SUBJECTSBETWEEN SUBJECTS
DESIGNSDESIGNS
Different subjects take part in eachDifferent subjects take part in each
condition of the experiment, drawcondition of the experiment, draw
conclusions by makingconclusions by making
comparisons between thecomparisons between the
behaviors of different groupbehaviors of different group
subjects more than 1 or 2subjects more than 1 or 2
subjects are necessary.subjects are necessary.

4. SELECTING ANDSELECTING AND
RECRUITING SUBJECTSRECRUITING SUBJECTS
●●The more the sampleThe more the sample
resembles the wholeresembles the whole
population, the more likely itpopulation, the more likely it
is that the behavior of theis that the behavior of the
sample mirrors that of thesample mirrors that of the
population.population.

5. ●●Encouraging volunteers byEncouraging volunteers by
making experiment seem:making experiment seem:
*Appealing / interesting*Appealing / interesting
*Non threatening*Non threatening
*Meaningful*Meaningful
*Get someone known the subjects to ask them, preferably a*Get someone known the subjects to ask them, preferably a
woman of high status.woman of high status.
*Emphasize the responsibility of people to aid in research that*Emphasize the responsibility of people to aid in research that
can help others and point out that lots of people do it.can help others and point out that lots of people do it.
*Give them reinforcement (money & gifts)*Give them reinforcement (money & gifts)

6. HOW MANY SUBJECTS?HOW MANY SUBJECTS?
*If individuals in the populations*If individuals in the populations
are all very similar get a smallare all very similar get a small
sample size.sample size.
*If individuals in the population*If individuals in the population
are likely to be different, get aare likely to be different, get a
large sample size.large sample size.

7. EFFECT SIZEEFFECT SIZE
An estimate of the size of theAn estimate of the size of the
treatment effect, fewer subjectstreatment effect, fewer subjects
necessary to detect treatmentnecessary to detect treatment
effect, advisable to have at leasteffect, advisable to have at least
15-20 subjects, small number15-20 subjects, small number
make effect hard to detect.make effect hard to detect.