Experimental Design

3.2.3 Research Methods

independent groups

each participant is allocated to a group and participates in one experimental condition » data from each group is independent of the other

repeated measures

each participant completes all conditions » data is related due to individual performance differences

matched pairs

participants are paired up based on variables relevant to the experiment; each half of the pair is randomly allocated to a condition

strengths of independent groups

• order effects cannot be observed

• less time-consuming to collect data as experiments can be carried out simultaneously

• participants less likely to guess aims

weaknesses of independent groups

• risk of participant variables affecting results, reducing internal validity

• difficult and time consuming to recruit different participants to each condition

ways to reduce the impact of participant variables in independent groups

• random allocation of participants to evenly distribute participant variables

• large sample size

strengths of repeated measures

• no participant variables » high internal validity

• fewer participants need to be recruited

order effect

how the sequence of conditions in a repeated measures design affects participant performance

weaknesses of repeated measures

• risk of order effects impacting the results, as participants may become better or worse at the task with experience

• high chance participants will figure out the study’s aim » increases demand characteristics

way to reduce order effects

counterbalancing: each group has a different order to complete the conditions in

strengths of matched pairs

• participants only complete one condition » demand characteristics reduced and no order effects

• risk of participant variables affecting results is reduced » increases internal validity

weaknesses of matched pairs

• expensive and time consuming to match up participants

• difficult to match up participants identically