experimental design

define experimental design

the different ways in which the testing of participants can be organised in relation to the experimental conditions (how participants are arranged in relation to the different experimental conditions)

what are the three experimental designs?

repeated measures, independent measures, matched pairs

what are independent groups?

• participants only preform in one condition of the experiment

evaluation of independent groups?

strengths

• only preform in the one condition- makes it less likely that the participants will find out the aim of the study - decreases the risk of demand characteristics and increases the validity of the experiment

• only preform in one condition - avoids order effects (fatigue, boredom practise)

limitations

• different participants used for each condition - participant variables are not controlled - could act as an extraneous variable

• requires more people- not economical + time consuming

what are repeated measures?

the same participants are used in each condition

evaluation of repeated measures

strengths

• same participants used - comparing same people - controls participant variables + are removed as an extraneous variable

• fewer participants needed- more economical and less time consuming

limitations

• all participants do all conditions - causes order effects (pps could be affected by boredom fatigue and practise)

• all pps take part in all conditions - they have more information on the study - increases risk of demand characteristics

what are matched pairs?

Pairs of participants are matched on some variables that may affect the DV. One member of each pair is assigned to condition A and the other to condition B

evaluation of matched pairs

strengths

• pps only take part in one condition -- less likely to interpret cues and respond to demand characteristics

• avoids order effects because pps only take part in one condition

limitation

• impossible to match pps exactly + is very time consuming + expensive as pre-tests are required (there has been attempts to make pps more similar but people ca never be matched exactly) so there is a possibility of participant variables