sampling techniques Flashcards
what are the stages of the sampling process ?
stage 1 : define target population stage 2: select sampling frame stage 3: choosing a sampling technique stage 4: determine sample size stage 5: collect data stage 6: asses response rate
what is a sampling frame ?
a list of the actual cases from which sample will be drawn
how is a sampling unit defined?
inclusion criteria
exclusion criteria
what are the two main types of sampling techniques ?
random sampling
non-random sampling
what does probability or random sampling mean ?
means that the sampling unit in the population has an equal chance of being included in the sample
what is the first step in random sampling ?
constructing a sampling frame first
what is the greatest advantage of probability sampling or random sampling ?
free from bias
what are the types of random sampling ?
simple random sampling systematic random sampling stratified random sampling cluster sampling multi stage sampling
when is it best to use systematic random sampling ?
if the study population is homogenous and you have a complete list of all the units
what is the method of systematic random sampling ?
- population size is to be determined
- sample size needs to be determined
divide pop size by sample size to get the interval
choose a number within the interval
then add the interval to that number and so on
what is the disadvantage of systematic random sampling ?
risk of bias due to cyclic phenomenon
what is stratified random sampling ?
the population is separated into strata according to a certain criteria and a random sample is taken from each group
the sub samples are then joined to form a total sample for the study
when is stratified random sampling used ?
when there is a lot of variation within a population
what is cluster sampling ?
whole population is divided into clusters or groups, then a random sample is taken from these clusters
when is it best to use cluster sampling ?
for researchers whose subjects are fragmented over a large geographical are as it saves time and money
what is non probability sampling often associated with ?
case study research design and qualitative research
what are the types of non probability sampling ?
quota sampling
snowball sampling
convenience sampling
judgemental sampling
what is quota sampling ?
participants are chosen on the basis of predetermined characteristics
what is snowball sampling ?
non random sampling that uses a few cases to help encourage other cases to take part in a study
what is convenience sampling ?
selecting participants because they are often readily and easily available
what is judgemental sampling ?
particular persons or events are selected deliberately in order to provide important information that cannot be obtained from other choices
what is the relationship between sample size and sampling error ?
as the sample size increases the sampling error decreases
what are the factors that must be taken into consideration when calculating sample size ?
type 1 error
type 2 error
the power of a study
what is a type 1 error ?
the risk of a false positive result (( chance of detecting a statistically significant difference when there is no real difference)
what is a type 2 error ?
the risk of a false negative result ( the likelihood of not detecting a significant difference when there is a difference)
what is the power of a study ?
the probability of not making a type 2 error
what determines the power of a study ?
- the frequency of the condition
- the magnitude of the effect
what does the sample size reflect ?
the number of obtained responses and not necessarily the number of questionnaires distributed
what is the response rate ?
the number of cases agreeing to take part in the study
