experimental design

• An independent groups design is when two separate grous of pps experience two different conditions of the experiment.
• strength of independent groups

  -order effects are avoided (when pps become aware of or bored with an experimental procedure)

  -there are less likely to be demand characteristics because pps only take part in 1 condition of the experiment and are therefore less likely to pick up on cues.
• weakness of independent groups

  -individual differences between groups (pps variable) may affect the results, to deal with this random allocation is used.

  -larger amount of pps are needed in this experimental design.
• repeated measure design is where all pps take part in both conditions.
• strength of repeated groups

  -pps variable problems are avoided as all pps takee part in both conditions. it doesnt matter if they have different abilities as they are kept constant through both conditions.

  -requires fewer pps as the same group is re-used.
• weakness of repeated groups

  -order effects are very likely to occur, pps may become bored, aware of aims or tired as they carry out a task twice. They would need to control this by using counterbalancing.

  -demand characteristics are more likely to occur as pps have been exposed to both conditions of the experiment so may pick up on cues or figure out the aim of the experiment.

  -researcher will need to ensure they have different test materials for condition 1 and 2
• counterbalancing is an attempt to control order effects in which half the pps take part in condition A then B, and the order half take part in condition B then A
• counterbalancing does not remove or prevent order effects but attempts to balance out the effects of order between the two conditions.
• matched pairs design is where pairs of pps are first matched on a key variable. Then one member is assigned to condition A and the other assigned to condition B.
• strength of matched pairs

  -issue of pps variables is greatly reduced.

  -order effects are totally avoided

  -demand characteristics less likely
• weakness of matched pairs

  -pretty much impossible to match pps exactly on every characteristics unless maybe they are identical twins-usually just matching physical characteristics

  -very time-consuming to find lots of people that match each other so closely.