MIR (Experimental Design)

MIR (Experimental Design)

1. Matched Pairs

   • If you have two groups ... each group would have the same amount of boys as girls. They would do different things but they would be match for example same levels of IQ
   • disadvantages - Very time consuming and difficult to match all of your participants in this way
     • It is impossible to match people for all characteristics even if you were to use MZ twins between the two groups! There would be extraneous variables
   • advantages: No order effects since each participant only does the task once
     • You can use the same material twice
       • Groups are similar in terms of individual characteristics

2. Repeated measures design

   • Use the same participants in each group or condition
   • advantages - The two groups have the same age, sex, personality, ideas, past experiences, IQ, reaction times (crucially for this one) etc. They are perfectly matched. They are the same people!
   • Disadvantages - Order effects: Assuming, as we expect the group do better on the second day, can we be sure that this increase in performance is due to the coffee? It could be that they’ve had the chance to practice the task the day before! It’s not surprising they’re better the second time around. This is called order or practice effect.
     • Boredom: Of course, on some tasks it could work the other way, and a task done the second time shows a deterioration because they’re fed up with doing it.

3. Independent measures design

   • Different people allocated to different groups therefore two groups can happen at the same time
   • Disadvantages: Participants are not matched in terms of IQ, personality, age etc.
     • You will need twice as many participants.
   • Advantages: No order or practice effects
     • Can use the same stimulus material (such as word lists in memory) for each group