what is an experimental design
this is the different ways in which Ps can be organised in relation to experimental condition e.g. the ways in which Ps are used in experiments
what is Independent measure design
this is when two separate groups of Ps experience two different conditions in an experiment
so if there are two levels of the independent variable it means that participants experience one level of the IV only
explain independent measure in the speedupp scenario
one group of Ps= drinking the energy drink i.e. condition A the experimental condition
another croup is drinking water i.e. condition B in the control condition
the performance of the two groups would then be compared. In this case, we would compare the difference in the mean number of words spoken in a 5 min period after drinking for each group/condition
What is a repeated measures design ?
all participants take part in all conditions
describe a repeated measures design with condition A experimental and condition B control
each participant would first experience condition A (drinking the energy drink)
each participant would then later experience condition B ( drinking water)
following this the two mean scores from each condition would be compared to see if there was a difference
What is matched pairs
this is when pairs of Ps are first matched on some variable(s) that may affect the dependant variable
Then one member of each pair is assigned to Condition A and the other pair to condition B
This is an attempt to control the confounding variable of participant variable
explain how matched pairs can be used in memory tests
in a memory test participants can be matched to IQ as this might be a good indicator of their ability to recall information
the participants with the 1st and 2nd highest IQ will be paired up
then the 3rd and 4th highest IQ will be matched and so on
then the participant from each pair would be allocated a condition in the experiment
this methods often necessitates the use of pre-test if matching is to be effective
What is random allocation ?
this is an attempt to control for participant variables in an independent group's design. This ensures that each participant has the same chance of being in one condition as any other.
What is counterbalancing ?
an attempt to control for order effect in a repeated measures design: half the Ps experience the condition in one order and the other half experience the condition in the opposite order.
what are the a disadvantage of independent group design to do with participant variables ?
and explain how this may effect the validity of the experiment
The participants that occupy the different groups are not the same in terms of Participant variables I.E one group of Ps are more chatty than the other -speedupp example
If the researcher finds a difference between the groups on the DV this may be more to do with the participant variables than the IV
This acts as a confounding variable reducing the validity of the findings
How does random allocation reduce participant variables
It means that participants are randomly allocated to different experimental groups in an attempt to evenly distribute participant variables/characteristics across the condition
What is another disadvantage of Independent measures ?
less economical than repeated measures as each Ps contributes to only a single result
Twice as many participants would be needed to produce equivalent data to that collected in a repeated measures design
increases the time and money spent on recruiting participants
What is a strength of using Independent measures ?
order effects are not an issue as they only take part in one condition this also means Ps are less likely to guess the aim of the study
What is a disadvantage of repeated measures design
each Ps has to do at least 2 tasks and the order of these tasks may be significant
order effects also arise because repeating two tasks may create boredom or fatigue that could cause a deterioration in performance on the second task- so the order in which the tasks are in are important
Ps may also improve at the second task through the effects of practice especially on skill based tasks
Ps are more likely to work out the aim of the study when they are experiencing all conditions of the experiment
order =confounding variable
How does counterbalancing help with oder effects ?
half the Ps take part in condition A -B
and the other half take part in condition B-A
it tries to balance out effects of participant variables
what is a strength of repeated measures design
participant variables are controlled therefore higher validity and fewer participants are needed therefore less time and money spent on recruiting
What is an advantage of matched pairs ?
participants only take part in a single condition so order effects and demand characteristics are less of a problem
What are the diadbatages if matched pairs ?
Although there is some attempt to reduce Ps variables in this design Ps can never fully be matched exactly
Even when identical twins are used in matched pairs, there will still be important differences between them that may effect the DV
this is also time-consuming and expensive, especially if pre-tests are required, so this less economical than other designs