Sampling Methods:
Random –
Every member of the population has a chance of selection
Technique: all participants’ names in a hat, required number drawn. Or, names
given a number and participants chosen using random number generator
Pros: unbiased, all members have a chance of selection
Cons: takes more time and effort as full list of population needed
Systematic –
Select every Nth person from a list, eg. 5th
Technique: use a predetermined system, such as selecting every 20th person
from a phonebook
Pros: unbiased, selection is objective
Cons: not everyone selected will agree to take part
Stratified –
Participants are selected according to frequency in population
Technique: subgroups or strata are identified and participants are chosen
according to their frequency in population eg. if population is 50%
male/female, sample is 50% male/female
Pros: likely to be more representative
Cons: subgroup selection may be biased
Opportunity –
Selecting people who are most available at time of study
Technique: asking most accessible people eg. on the street at work, uni etc.
Pros: easiest method, quick
Cons: biased as sample is only from part of targeted population
Volunteer –
Individuals select themselves and contact researcher
Technique: experiment advertised in newspaper, noticeboard etc.
Pros: large range of possible participants, easy
Cons: volunteer bias, only certain types of people will agree to take part eg.
helpful people
Random –
Every member of the population has a chance of selection
Technique: all participants’ names in a hat, required number drawn. Or, names
given a number and participants chosen using random number generator
Pros: unbiased, all members have a chance of selection
Cons: takes more time and effort as full list of population needed
Systematic –
Select every Nth person from a list, eg. 5th
Technique: use a predetermined system, such as selecting every 20th person
from a phonebook
Pros: unbiased, selection is objective
Cons: not everyone selected will agree to take part
Stratified –
Participants are selected according to frequency in population
Technique: subgroups or strata are identified and participants are chosen
according to their frequency in population eg. if population is 50%
male/female, sample is 50% male/female
Pros: likely to be more representative
Cons: subgroup selection may be biased
Opportunity –
Selecting people who are most available at time of study
Technique: asking most accessible people eg. on the street at work, uni etc.
Pros: easiest method, quick
Cons: biased as sample is only from part of targeted population
Volunteer –
Individuals select themselves and contact researcher
Technique: experiment advertised in newspaper, noticeboard etc.
Pros: large range of possible participants, easy
Cons: volunteer bias, only certain types of people will agree to take part eg.
helpful people
