There are several sampling techniques to use for a questionnaire. Each has pros and cons that can affect the results of the study. The authors are from University College London.
Parameters:
(1) target (group vs general population)
(2) accessibility of the target group
(3) sample random and representative of target
|
Target |
Accessible |
Sampling |
Type |
|
group |
yes |
nonrandom |
opportunistic (haphazard) |
|
group |
limited |
nonrandom |
snowball |
|
group |
yes |
random |
random |
|
group |
limited |
random |
cluster |
|
general population |
some easy, some limited |
random in nonrandom group |
quota |
|
Type |
Sampling |
Useful for |
|
opportunistic |
whoever is available at a given moment or event |
easiest to conduct but subject to bias |
|
snowball |
recruited members of selected group identify others to take part |
hard to reach groups |
|
random |
randomly from group |
representative of whole group |
|
cluster |
randomly from a selected subgroup (cluster) |
when the number of subjects who can be contacted is limited |
|
quota |
subjects selected to meet quotas for each population component |
representative of population as a whole |
