Market Research-Sampling
Definition
Sampling means getting opinions from a number of people, chosen from a specific group, in order to find out about the whole group.
Sample Design
Sample Size
key factors
No estimate taken from a sample is expected to be exact
To lower the margin of error usually requires a larger sample size
The confidence level is the likelihood that the results obtained from the sample lie within a required precision
Population size does not normally affect sample size
Types of Sampling
Cluster sampling
Convenience sampling
Judgement sampling
Quota sampling
Units in the population can often be found in certain geographic groups or "clusters"
Advantages
Quick and easy
Doesn't need complete population information
Good for face-to-face surveys
Disavantages
Greater risk of sampling error
Expensive if the clusters are large
Advantages
Subjects are readily available
Large amounts of information can be gathered quickly
Disadvantage
Prone to volunteer bias
The sample is not representative of the entire population, so results can't speak for them - inferences are limited. future data
A deliberate choice of a sample - the opposite of random
Advantage
Good for providing illustrative examples or case studies
Disadvantage
Very prone to bias
Cannot extrapolate from sample
Samples often small
The aim is to obtain a sample that is "representative" of the overall population.
Method of selection
Plans for analysing and interpreting the results
Sample structure
Disadvantage
Advantage
Quick and easy way of obtaining a sample
Not random, so some risk of bias
Need to understand the population to be able to identify the basis of stratification
Simply random sampling
This makes sure that every member of the population has an equal chance of selection.
Advantage
Disadvantage
Can calculate both estimate of the population and sampling error
Simple to design and interpret
Need a complete and accurate population listing
May not be practical if the sample requires lots of small visits over the country
Systematic sampling
After randomly selecting a starting point from the population between 1 and *n, every nth unit is selected.
Advantage
Disadvantage
Easier to extract the sample than via simple random
Ensures sample is spread across the population
Can be costly and time-consuming if the sample is not conveniently located