define target population
total collection of ppl who share given set of characteristics.
eg all students registered for As Psychology exams in 2010 in the UK
a selection of individuals from the target pop, which shares all the main characteristics of the pop despite its smaller size
An indication of the extent to which a sample differs from the target pop.
a way of selecting a grp of p's because they are available & fit for the criteria needed for them to take part in a rsh study.
a group of p's who are invited & agree to take part in a rsh study (self selected)
This can occur if a certain kind of p' is persistently recruited for rsh at the expense of others.
Therefore other subgrps are not adequately represented in the body of psycho knowledge.
a target pop is divided into subgrps & op samples are taken frome each of them in the same proportions that exist in the target pop.
Stratified Random Sampling
a target pop is divided into subgrps & random samples are taken from each of them in the same proportions that exist in the target population.