experiments - experimental designs

Question 1

3 types of experimental design

Answer 1

• independent groups design
• matched pairs
• repeated measures design

Question 2

independent groups design AO1

Answer 2

• ppts take part in one condition only
• each condition = different ppts

how it is conducted
- ppts recruited
- split into equal sized groups
- allocated conditions

Question 3

independent groups design strength

Answer 3

• no order effects
• ppts take part in one condition only CONTEXT
• not bored/fatigued
• UNLIKE repeated measures design where ppts take part in all conditions

Question 4

independent groups design limitation

Answer 4

• individual differences
• e.g.one group may be much better at task than the other CONTEXT
• lowers internal validity
• unlike repeated measures
• same ppts take part in all conditions

Question 5

repeated measures AO1

Answer 5

• ppts take part in all conditions
• same ppts in same conditions

how to conduct
- recruit ppts
- all take part in 1 condition
- time delay e.g. 1 hour
- all take part in second condition
- conditions different but measuring same DV

Question 6

repeated measures strength

Answer 6

• individual differences removed
• same ppts take part in same conditions - CONTEXT
• changes in DV can be due to IV not any other variables
• increasing internal validity
• UNLIKE independent groups design
• where individual differences can effect DV

Question 7

repeated measures limitation

Answer 7

• order effects
• ppts may become bored/fatigued/tired
• may perform worse in second condition
• or better due to practice OR lasting effects between conditions - CONTEXT
• UNLIKE independent groups design ppts take part in one condition only
• IGD = no order effects

Question 8

matched pairs AO1

Answer 8

• ppts matched in pairs on same characteristic e.g. IQ/age
• given appropriate test and matched with ppt with same score
• each member of pair randomly allocated across each condition

how to conduct
- choose variable to match ppts on
- give them appropriate test before study
- match based on test scores
- randomly allocate each member of pair to random condition

Question 9

matched pairs AO3
strengths

Answer 9

• individual differences reduced
• ppts matched on same characteristics e.g. IQ/age - CONTEXT
• can be more sure that changes in DV is due to IV
• increasing internal validity
• unlike IGD
• no order effects
• ppts take part in same condition
• not get bored/tired/fatigued between conditions CONTEXT
• unlike repeated measures

Question 10

independent groups design problem

Answer 10

• individual differences between participants
• different ppts in different conditions
• ppts may have traits that make them better at the DV CONTEXT
• lowering internal validity

Question 11

independent groups design control

Answer 11

• random allocation
• ensures same chance of ppts being in both conditions
• unlikely all ppts in one condition share same characteristic to make them better at DV

HOW
1. write names of ppts on paper
2. place all names in hat
3. randomly pick out names place one in condition 1 and one in condition 2 - CONTEXT

Question 12

repeated measures problem

Answer 12

• order effects
• ppts take part in both conditions
• long lasting effects between conditions CONTEXT
• e.g. bored/tired/fatigued
• may perform worse
• or better due to practice

Question 13

repeated measures design control

Answer 13

• counterbalancing
• to reduce order effects

HOW
1. half ppts complete condition A then condition B
2. half ppts complete condition B then condition A
3. balanced order effects