research methods - experimental design

what is an experimental design

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