research methods: experimental design Flashcards
What are the 4 designs?
independent groups, repeated measures, matched pairs
Independent groups
Definition/describe:
How to conduct it:
Ppts take part in one condition
only. Each condition has different
group of Ppts.
*A group of ppts are recruited.
*They are then split into equal
sized groups.
*A different group is allocated
each condition.
independent groups
Ao3- advantage
There will be no order effects as ppts
only take part in one condition so they
will not get bored/fatigued or better at
the task/have lasting effects from one
condition to the next (CONTEXT) UNLIKE
repeated measures design where ppts
take part in all conditions and could have
order effects.
Can be used when repeated measures
design is inappropriate (e.g. quasi
experiments when looking at gender
differences) (CONTEXT) as each
condition needs different Ppts.
independent groups
disadvantages
Individual differences may affect the
DV as there are separate groups of Ppts
in each condition e.g. some Ppts could
have a better memory which wouldn’t
be suitable in a memory study
(CONTEXT) lowering the internal
validity UNLIKE repeated measures that
uses the same group of indivudals in all
conditions to reduce the effect of
individual differences.
More Ppts are needed as two different
groups are required for the different
conditions (CONTEXT) UNLIKE repeated
measures where you use less ppts as
every ppt takes part in all conditions.
Repeated measures
Definition/describe:
How to conduct it:
All ppts take part in all/both
conditions of the experiment.
*pts complete one condition.
*After a sufficient time lapse (an
hour) they will complete the other
condition.
*The task (DV) should be different
but matched on
difficulty/measuring the same
thing.
Repeated measures
advantages:
Individual differences between
participants in each condition are
removed e.g. IQ as potential confounding
variables, as the same Ppts take part in
all conditions (CONTEXT). Therefore, the
researcher can be more sure that any
changes in the DV are due to the IV and
not any other variable increasing the
internal validity of the research UNLIKE
IGD that will use different ppts in
different conditions so individual
differences could affect the DV.
Requires fewer participants as the same
Ppts take part in all conditions
(CONTEXT) UNLIKE in an independent
measures design as separate groups are
needed for separate conditions.
Repeated measures
limitations
Order etfects may occur when participants
take part in more than one experimental
condition they may perform worse in the
second condition (due to boredom or
fatigue) or better in the second condition
(due to practice), or there may be lasting
effects from condition 1 to condtion 2
(CONTEXT) lowering the internal validity
UNLIKE independent measures where ppts
only take part in one condition so cannot
be susceptible to order effects.
Increased chances of demand
characteristics as participants take part in
all conditions. They may pick up on clues
given off by the researcher as they spend
much more time with them, or from the
research situation
, and change their
natural behaviour to help or hinder the
research (CONTEXT) lowering the internal
validity, UNLIKE IGD where ppts are less
likely to pick up on clues as the only take
part in one condition of the research
matched pairs
Definition/ describe:
How to conduct it:
pts are matched on important
characteritsics in the study e.g.
age or IQ. By giving them an
appropriate test and matching two
ppts with the same score.
Each member of the pair is then
randomly allocated across each
condition
*Choose a variable to match ppt
on
*Test the ppt on this variable
before the study
atch ppt with the same
scores
matched pairs
advantages
reduces individual differences between participants as it matches ppts on variables important to the reserach, such as IQ/age/happiness. (CONTEXT)
Therefore, the researcher can be more
sure that any changes in the DV are due
to the IV and not any other variable.
UNLIKE in an independent measures
where separate ppts are in separate
conditions.
There will be no order effects as ppts
only take part in one condition so they
will not get bored/fatigued or better at
the task/have lasting effects from one
condition to the next (CONTEXT) UNLIKE
repeated measures design where ppts
take part in all conditions and could have
order effects.
matched pairs
limitations
Very time consuming to match up and
find similar participants. (CONTEXT)
especially if a pre-test is needed to
match ppt on a certain characteristic.
The psychologists would need a very
large pool of people UNLIKE repeated
measures design where you use the
same ppts in all conditions.
(E
ve
Individual differences cannot be fully
eliminated. Psychologists match ppts
on variables important for the research
but are not able to match ppts on all
variables (CONTEXT). Therefore this
could question the validity of the
matched-pairs design. UNLIKE RM
where each condition will use the same
ppt therefore, indivudal differences
will be eliminated.
How to control for individual differences in independent groups design?
Control: Random allocation
WHY:
This ensures that each Ppt has the same chance of
being in one condition as any other condition,
therefore it is unlikely that all ppts in one
condition will share a characteristic to help them
perform better at the DV.
HOW:
1.
2.
3.
Write the names of the ppts on equal sized
pieces of paper.
Put the paper in a hat
Then randomly pick out ppts names an
place half in condition 1 and the other half
in condition 2 (CONTEXT).
How to control for order effects in repeated measures design?
Control: Counterbalancing (ABBA) method.
WHY:
To control and reduce order effects
HOW:
1.
Half the Ppts complete condition A then
condition B. (CONTEXT)
2.
The other half complete condition B first
then condition A
3.
Order effects are balanced/distributed
across both conditions.
Top tip: Never say order effects have been
eliminated……they haven’t!!
