experiments - experimental designs Flashcards
3 types of experimental design
- independent groups design
- matched pairs
- repeated measures design
independent groups design AO1
- ppts take part in one condition only
- each condition = different ppts
how it is conducted
- ppts recruited
- split into equal sized groups
- allocated conditions
independent groups design strength
- 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
independent groups design limitation
- 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
repeated measures AO1
- 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
repeated measures strength
- 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
repeated measures limitation
- 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
matched pairs AO1
- 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
matched pairs AO3
strengths
- 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
independent groups design problem
- individual differences between participants
- different ppts in different conditions
- ppts may have traits that make them better at the DV CONTEXT
- lowering internal validity
independent groups design control
- 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
repeated measures problem
- 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
repeated measures design control
- 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