Spontaneous behavior is recorded in a natural setting.
The observer has direct contact with the group of people they are observing.
The researcher tells the group he or she is conducting research (i.e. they know they are being observed).
A stratified sample is a mini-reproduction of the population. Before sampling, the population is divided. For example, by gender, social class, education level, religion, etc. Then the population is randomly sampled within each category. If 38% of the population is college-educated, then 38% of the sample is randomly selected from the college-educated population.
Participants 'self select' themselves by responding to an invitation.
Volunteers could have different characteristics to non volunteers.
BPS code of conduct
Right to withdraw