There are many ways of using observation as method of collecting data and studying participants.   


Naturalistic observation


Naturalistic observation is a type of observational study where participantsí spontaneous behaviour is recorded in their own environment.  Interference is kept to a minimum and therefore such studies are said to have high ecological validity. 


However, because variables are not manipulated they are said to lack control.  This lack of control makes replication difficult and there are also risks of observer bias and ethical issues of invasion of privacy.


Controlled observation


Controlled observation is a type of observational study where the conditions are contrived by the researcher.   This type of observation may be carried out in a laboratory type situation and because variables are manipulated is said to be high in control.   The Dement and Kleitman study is an example of controlled observation.   The weakness of the method is that it will be low in ecological validity compared to naturalistic observation.   If participants are aware they are being studied they behave differently.



Participant observation


Participant observation is a type of observational study where the observer is also a participant in the activity being observed.  This may be with or without the participantsí knowledge.   If the researcher is undisclosed the study should be high in ecological validity and very in-depth and detailed information can be gained.  The Rosenhan study is an example of participant observation.   However, participant observations may be hard to carry out, especially when trying to record behaviour without the participants becoming aware.  The researcherís presence may alter the participantsí behaviour and there are problems of bias as the observer may become very involved with the participants.