The Experiment

Types of Experiment

1. Laboratory 
2. Field
3. Natural

Laboratory Experiment

- Laboratory environment
- experimentor can control situational and participant variables

Examples
"The Strange Situation"
"Harlow's Monkey's"
"Pavlov's Dog's"




Advantages
- demonstrates clear cause and effect
- easily control extraneous variables
- objective measures ensure validity
- allows replication


Disadvantages 
- low ecological validity
- impossible to control all random variables
- demand characteristics
- sample bias






Field Experiment

- Takes place in an outdoor/indoor real life setting.

Examples 
"Glasgow Study" Shaffer and Emerson


Advantages
- high ecological validity
- low demand characteristics
- avoids sample bias


Disadvatages
- less control of extraneous variables
- diffcult to replicate
- ethics : consent, privacy, deception







Natural Experiments


- semi-experiment
- cannot manipulate IV
- experimenter measures DV

Example
Hodges and Tizard


Advantages
- high ecological validity
- no sampling bias
- low demand characteristics


Disadvantage
- no control of IV
- no control of extraneous variables
- cannot replicate unless naturally occuring
- ethics : consent, privacy, deception






Experimental Designs
  

1. Independant Measures
2. Repeated Meaures
3. Matched Pairs

Independant Measures

- Participants only undergo one condition of the experiment.
- Randomly allocated to the experimental or controlled group
- Ideal when there are two IV conditions


Example
Test whether people stop for strangers
1. tramp
2. buisness man




Advantages 
-Quick
-Cheap
-Easy
-No order effect
-good for experiments involving deception




Disadvantages
- less control of participant variables
- large sample size





Repeated Measures

- Participants do both conditions of the experiment to test themselves
- Eliminates participant variables


Practise Effect - people do better the second time around. Must be the same both times or this will be an extraneous variable.


Boredom Effect - self explanitory


Counterbalancing

Half of participants do first condition, the other have do the second condition.
They then swap to do the other condition they have not already done.
Can eliminate order effect.






Advantages
-eliminates individual differences
-twice amount of data with small sample size




Disadvantages
- cannot be used when subjects must be different (men and woman)
- order effects
-boredom effects
-practise effects
- need to counterbalance



Matched Pairs

- Participants matched with someone of the same intelligence, score, ability etc.
- Identical twins the best!
- Used to avoid participant variables and order effects.


Advantages
- good for misleading experiments
-eliminates individual differences
-no order effects


Disadvantages 
- cannot perfectly match participants on ALL variables
-big sample size