4. OUTCOMES:
Define population
Define sample
Describe the process of sampling procedures including
random, stratified and random stratified
Describe the process of participate allocation to groups
(experimental and control) including random allocation
Discuss the advantages and disadvantages of different
experimental designs including repeated measures, matched
participants and independent groups
Describe the placebo effect and ways of managing its
occurrence
Describe the experimenter effect and ways of managing its
occurrence
Monday, 14 January 2013
5. Sampling
Sampling is the selection of participants for a
research.
Population refers to the group which the research
wishes to draw conclusions from.
The term sample refers to the members of the
population that have been chosen to take part in the
research.
Sampling procedures must ensure that the sample is
representative of the population.
Monday, 14 January 2013
6. Representative Samples
Two techniques are used to
ensure a representative sample:
1)Random Sampling
2)Stratified Sampling and
Stratified Random Sampling.
Monday, 14 January 2013
7. Random Sample
A sampling procedure in which every member
of the population has an equal chance of
being selected
Examples include:
1) Picking a name out of
a hat
2) Tattslotto
3) Closing my eyes and
selecting a number to
match that number with
student id numbers.
Monday, 14 January 2013
8. Stratified Sampling and Stratified
Random Sampling
Is used when you wish to
eliminate the effects of
confounding variables.
The effects of a certain
variable can be eliminated as a
possible confounding variable
in an experiment.
The variable could be any
personal attribute, such as
age, years of education,
ethnicity, gender, IQ etc.
Monday, 14 January 2013
9. Activity:
Stratified Random Sampling
Monday, 14 January 2013
10. Participant Allocation: Experimental &
Control Groups
The experimental method uses two different groups
called the experimental and control groups.
The experimental group are exposed to the IV, known
as the ‘treatment’.
The control group do not receive the treatment (IV).
The purpose of the experimental group is to show the
effects of the IV on the value of the DV.
The purpose of the control group is to form a basis for
comparison with the experimental group.
Monday, 14 January 2013
11. Experimental and Control Group Allocation
It is super important that all participants have an
equal chance of being in the experimental or control
group. That is Random Allocation.
When there is a large enough sample, both the
experimental and control groups will be equivalent on
all participant characteristics therefore the presence
or absence of the IV is the only difference between
them.
E.G. If we had all males in the experimental group and
all females in the control group, then an obvious
extraneous variable will be gender.
Monday, 14 January 2013
12. Experimental Designs
There are three popular experimental
designs
Repeated Measures Design
Matched Participants Design
Independent Groups Design
Monday, 14 January 2013
13. Repeated Measures Design
(within participants design)
• In a repeated measures design all participants experience both
the experimental and control groups.
• This is possible by conducting the experiment on two
occasions and then comparing the two results.
Monday, 14 January 2013
14. What are the advantages of repeated measures design?
What are the limitations (disadvantages)?
Monday, 14 January 2013
15. Matched Participants Design
• Enables the researcher to identify a variable that is likely confound and to
eliminate the effects of this variable from the experiment.
• Participants can be ranked in accordance with their scores on this variable
Monday, 14 January 2013
16. • For example
• A sports coach developed a new game plan that would help
the team reach the playoffs. He decided to test this by giving
the experimental group the instruction but not the control
group. Because individual skills would be a confounding
variable, he decided to ‘match’ the groups. The two highest
skilled players will be randomly allocated to either the
experimental or control group, the third and fourth most
skilled will then be randomly allocated to either and so on and
so forth until all players were allocated to a group resulting in
the same mean skill percentage in both groups.
Monday, 14 January 2013
17. What are the advantages of matched participants design?
What are the limitations (disadvantages)?
Monday, 14 January 2013
18. Independent Groups Design
(between participants design)
• Allocates participants to the experimental or control group
at random
Monday, 14 January 2013
19. What are the advantages of independent groups design?
What are the limitations (disadvantages)?
Monday, 14 January 2013
20. Participants This may effect the DV
expectations resulting in invalid results
PLACEBO EFFECT
Can be eliminated by using single blind procedure, that is
participants are unaware of which group they are in.
Monday, 14 January 2013
21. For example: Experimenter treats
Experimenter participants differently depending on
influences the group they are in which in turn
experiment influences the behaviour of the
participant and effects the results
EXPERIMENTER EFFECT
Can be eliminated by using a double blind procedure, that is, neither
the experimenter or the participants are aware of whether they are
in the experimental or control group
Monday, 14 January 2013
