sampling Flashcards
Population
All the items of interest.
Census
Observes and measures every member or item of the population
Sample
A subsection of the population taken and measured to represent the whole population.
Census advantages and disadvantages
Advantages: Representative of the whole population and very accurate results.
Works well when the population is small.
Disadvantages: Time consuming and expensive.
Cannot be used when testing something that has to be destroyed in the process.
Hard to process the large quantity of data.
Sampling unit
One individual or item within the population
Sampling frame
When the sampling units are numbered or named then put into a list.
Simple random sample
Every member of the population has an equal chance of being picked. Using a sampling frame a set number of items/members are selected from the population to make a sample representing the whole population.
Systematic sampling
Members or items are selected at intervals on the sampling frame. If you want 20 in your sample and there are 100 in the population, select randomly a item between 1-5 then pick the next item to be sampled every 5th unit.
Stratified sampling
The population is divided into mutually exclusive strata and then a proportionate amount is randomly selected from each strata.
Simple sample advantages and disadvantages
Advantages: Not bias.
Easy and cheap.
Each sampling unit has equal chance of being selected.
Disadvantages: If sample size is large it can be time consuming and expensive.
A sample frame is needed.
Systematic sample advantages and disadvantages
Advantages: Simple and quick to use.
Suitable for large samples and large populations.
Disadvantages: A sampling frame is needed.
Can be bias if start value isn’t random or the sampling frame isn’t random.
Stratified sample advantages and disadvantages
Advantages: Sample accurately represents the populations structure.
Guarantees proportional representation.
Disadvantages: Population must be clearly into different strata.
Same disadvantages as simple random sample.
Quota sampling
The interviewer or sampler picks what reflects the characteristics of the whole population (not random). The population is divided into groups with similar characteristics. It is on a first come first served basis. Once the group of needed characteristics is full they ignore the rest.
Opportunity sampling
A study carried out asking people who meet the criteria and are available.
Quota sampling advantages and disadvantages
Advantages: Easy to get a represented sample with small sample.
No sample frame required.
Quick and easy.
Easy comparison.
Disadvantages: Not random.
Population must be divided into groups correctly.
