Experimental Designs

Independent groups design

Involves using different participants for each condition of the experiment

First advantage of independent groups design

Demand characteristics are less of a problem, participant only participants in one condition, less likely to guess the aim. The same materials can be used in both conditions

Second advantage of independent groups design

Order effects don’t influence a second condition, the participant only participates in one condition

First disadvantage of independent groups design

Participant variables differ, could act as extraneous variables unless controlled. May affect the results

Second disadvantage of independent groups design

More participants are required, it is less economical

A method to deal with the limitations of independent groups

Randomly allocate participants to conditions, distributes participant variables evenly

Repeated measures design

Using the same participants in each condition of an experiment

First advantage of repeated measures design

Participant variables could become extraneous variables, kept constant between conditions. The same participants are used in both conditions

Second advantage of repeated measures design

Fewer participants are required, more economical

First disadvantage of repeated measures design

Order effects may become constant errors when one condition is done after another

Second disadvantage of repeated measures design

Demand characteristics may be a problem, the participants do both conditions, have more clues to guess the aim. Can’t use the same materials, any task must be matched in difficulty

A method to deal with the limitations of repeated measures

Counterbalancing

Matched pairs design

Using different but similar participants in each condition of an experiment. The participants are matched in each condition in any important characteristics that might affect performance

First advantage of matched pairs design

Participant variables are kept more constant between conditions. Since the participants have been matched

Second advantage of matched pairs design

Order effects don’t occur, the participant only participates in one condition. Demand characteristics are reduced since participants are matched and take part in one condition

First disadvantage of matched pairs design

Participant variables can never be perfectly matched. Matching participants is very time consuming and difficult

Second disadvantage of matched pairs design

More participants are required, less economical

A method to deal the limitations of matched pairs

Restrict the number of variables to match on to make it easier. Conduct a pilot study, considers key variables that might be important when matching