Experimental design

• Independent group design - no order effects, only do one condition so not getting bored, increases internal validity, less chance of demand characteristics, less likely to work out the purpose of the study and change their behaviour to hinder or help which increases the validity of study. Individual differences such as gender or age, lower internal validity. Requires more participant than as the researcher will need to get two separate groups of ppts to end up with same amount of data.
• Matched pairs - no order effects, not become bored, increases internal validity, controls for individual difference, matched on age gender etc, increasing internal validity. most time consuming, need to identify participant variables and spend time matching ppts. Impossible to control all participant variables because only key ones can be matched for, could be others that effect the research so lowers internal validity.
• Repeated measures - requires fewer ppts as ppts take part in all conditions, meaning a potentially larger sample can be used, increasing external validity. Ppt variables removed increasing the internal validity. Results may be affected by order effects, ppts may become bored by second condition so do better or worse and lowers internal validity. Increased chance of demand characteristics as when ppts do the second condition they may work out the purpose of the study and change their behaviour and lowers internal validity.
• Repeated measures - strengths - participant variables removed, requires fewer participants. Weaknesses - affected by order effects and increased chance of demand characteristics. So, use counter balancing or multiple tests.
• Independent group design - strength - no order effects, less chance of demand characteristics. Weaknesses - individual differences/ participant variables, requires more ppts. So, random allocation to groups such as names in a hat.
• Matched pairs design - strengths - individual differences/ participant variables, no order effects. Weaknesses - impossible to control all ppt variables, time consuming. So, use alternative experimental design.