experiment design: evaluation Flashcards
what is a limitation of independent groups
the biggest issue with an independent groups design is that the participants who occupy the different groups are not the same
If the researcher finds a mean difference between the groups on the dependent variable (DV) this may be more to do with individual difference ( participant variables) than the effect of the IV
how can we reduce this limitation of independent groups design - how can we reduce the effect of participant variables
we can use random allocation to deal with this
- to address the problem or participant variables in an independent groups design, participants should be randomly allocated to the different experimental conditions
Random allocation attempts to evenly distribute participant characteristics across experimental conditions using random techniques
e.g. A and B written on piece of paper placed in a hat and the researcher selects them one at a time to assign participants to separate conditions
what is a limitation of repeated measures
the biggest issue for repeated measures is that each participants has to do at least two tasks and the order of these tasks may be significant ( there are order effects)
e.g.
in the energy drink example, having the energy drink first may have a continuing effect when a participant drinks water afterwards
how do we reduce order effect caused by repeated measures
we can use counterbalancing to deal with order effects
in counterbalancing, half the participants take part in condition A and B, and the other half take part in condition B then A as follows :
P1: A-B
P2: B-A
P3: A-B
how do order effects arise
order effects arise in repeated measures because repeating two tasks could create boredom or fatigue that might cause deterioration in performance on the 2nd tasks, so it matters what order the tasks are in
Alternatively, participant performance may improve through the effects of practice, especially on a skill - based task - in this case participants would perform better on the 2nd task
why are demand characteristics more likely in repeated measures
prarticpants are more likely to figure out the aim of the study when they experience all conditions of the experiment.
For this reason, demand characteristics tend to be more of a feature of repeated measures designs than independent groups
what is a strength of the repeated measures design
participants variables are controlled and fewer participants are needed
what is a strength of the matched pairs design
participants only take part in a single condition so order effects and demand characteristics are less of a problem
what is a limitation of the matched pairs design
- participants can never be easily matched.
Even when identical twins are used as matched pairs, there will still be important differences between them that may affect the DV - matching may be time - consuming and expensive, particularly if a pre - test is required, so this is less economical than either design.
