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Sampling Techniques and Sample size (Sampling Technique (Random (Cluster…
Sampling Techniques and Sample size
Sampling Technique
Random
Simple
Systematic
Stratified
Minimise the variability within each stratum and maximise the differences between strata
Particularly useful when the distribution of the characteristic of interest in the target population is skewed or when extremes are present
Cluster
Assume that all the clusters are basically identical with regard to the factors used to identify the clusters
In each chosen cluster, either choose all the elements or choose a random sample of elements
Particularly useful when the only sampling frame readily available is a list of clusters, not elements
Categorize the target population into clusters and then choose a random sample of clusters
every sampling unit in the target population has a known and equal chance of being selected
Non-random
Convenience
Useful in exploratory research for generating ideas, insights or hypotheses
Choice of elements is based on convenience and is entirely up to the person who does the sampling
Judgment
Choice of elements is based on the judgement of the researcher
market potential/ product testing/ merchandising displaying system
Quota
Stage 1: specify quota(s), so as to ensure that the composition of the sample is the same as the composition of the population with regard to the quota(s) of interest
Quotas, or control characteristics, can be demographic characteristics, specific attitudes or specific behaviours
Stage 2: elements, as long as they fit the quota(s), are chosen by using convenience or judgement sampling
A quota sample by itself cannot represent the population with any level of confidence
Snowball
More often used in occasions where the defined target population is small and unique and compiling a sampling frame is very difficult
The underlying logic is that small and unique groups of people tend to form their own social circles
Difference
List of the
population elements
Information about the
sampling units
Sampling skill
required
Time
requirement
Cost per unit
sampled
Accuracy
and reliability
Sample representativeness
Estimates of
population parameters
Measurement of
sampling error