Research design

* The same participants are used in both conditions of an experiment

+ Good control of participant variables

+ Fewer participants needed 

- Order effects : an extraneous variable that exists because of the order of conditions 

- Demand characteristics

* Two sets of participants are used,  one set for each condition

+ Lower risk of demand characteristics 

+ No order effects

- No control of participant variables

- More participants are needed

* Participants are matched together in terms of things such as IQ, each member of each pair is put into either the experiment or control group

+ No order effects

+ Patially control of participant variables

- Time consumin

- No one will ever match 100%

* Participants are selected by who is avaiable, normally students 

+ Easy and quick method

+ Sometimes the only mehod to use because of a short time frame

- BIASED 

- Can't generalise from an oppurtunity sample

* Participants respond to some kind of advertisement of your experiment e.g. newspaper ad

+ Sometime representative and varied

+ Already have partial consent

- Biased as it tends to be  a certain type of person who volunteers

- Normally an incentive needs to be given e.g. money

* Participants are selected using a random number technique e.g. pulling names out a hat

+ potentially unbiased

+ No experimenter bias of who takes part 

- Can be biased if people drop out

- Time consuming

* Selected using a predetermined system, every nth person

+ Unbiased

+ Objesctive system

- Not truely random, where do you start the pattern of every nth person?

- Time consuming  

* Subgroups are identified and participants are chose from these sub groups

+ representaive sample obtained 

- May be biased