Sampling Flashcards
What is Sampling?
A technique for selecting a representative subgroup of a larger population, accurately reflecting the distribution of a variable, to estimate something about it. (Person, Place, Time)
What is a Population?
- A group of people having one or more common characteristics living in a specific geographical location.
What is a Sampling Frame?
- The actual list of individuals that the sample will be drawn from.
- Needs to be complete and accurate; For the success of the study.
What are Sampling Units?
A single element or group of elements that are selected for a sample.
What is Sampling Variation?
The value can vary from sample to sample, depending on which sample is selected.
What is a Sampling Error?
- Arises out of random sampling.
- Statistical errors that arise when a sample does not represent the whole population.
Why do we need a sample?
- Save time and money.
- Unable to study all members of a population.
- Reduce bias.
- Measurements; better in sample than in entire population.
- Feasibility (Practicable)
How to sample?
In general, 2 requirements
- Sampling frame - available/develop one if not exist.
- Choose an appropriate sampling method to draw a sample from the sampling frame.
What are the Sampling Methods?
I. Probability sampling
- Every member of the target population has a known chance of being included in the sample.
II. Non-probability sampling
- The researcher selects samples based on their subjective judgment, rather than random sampling.
What is Simple Random Sampling?
(Type, Definition, Advantages, Disadvantages, Examples, How to do it[Techniques], and Select sample)
1 - Probability Sampling Method.
2 - Randomly selected subset of a population. (Equal Chance)
3 - Advantage
- Easy to do.
- Accurate representative.
- Removes all bias.
4 - Disadvantage
- Time Consuming
5 - Examples
-Pharmaceutical Patients (From a hospital record system.)
- Uni Students Selection.
6 - Techniques
- Lottery method
- Table of random numbers
7 - Selection;
- Define the population.
- Determine the desired sample size.
- List all members of the population or the potential subject.
What is Systematic Random Sampling? (Type, Definition, Advantages, Disadvantages, and Example.)
1- Probability Sampling Method
2- You sample every kth element from a population.
3 - Advantage
- Quick, Simplicity, and Convenience.
- Precision
4 - Disadvantage
- Over- or Under Representation.
- Risk of Data Manipulation.
5 - Example
- Every 25th name in a phone book.
What is Stratified Random Sampling? (Type, Definition, Advantages, Disadvantages, and Example.)
1 - Probability Sampling Method.
2 - Strata - Different Layers
- Population is divided into subpopulations and random samples are taken from each stratum (strata)
- Sample from each stratum should be proportional.
3 - Advantages
- Accurate
- Include sub-groups (Ensure representation of all groups of interest)
- Disadvantage
- Time Consuming
- Expensive
- Complex
- Examples
- Students from all grades (In a school study.)
- Ethnicity
What is Cluster (Area) Random Sampling?
(Type, Definition, Advantages, Disadvantages, Example, and Appropriate when)
1 - Probability Sampling Method.
2 - Researchers divide a population into smaller groups called clusters. They then form a sample by randomly selecting clusters.
3 - Advantage
- Quick.
- Less costly.
- Accurate.
4 - Disadvantages
- Biased samples
- High sampling error
- Examples
- Study the prevalence of obesity, health behaviour, or rare diseases across different communities or regions.
6 - Appropriate when;
- Can’t obtain a list of the members of the population.
- Have little knowledge of population characteristics.
- Population is scattered over a large geographic area.
What is Multistage Random Sampling?
(Types, Definition, Advantages, Disadvantages, Examples, and Stages)
1 - Profitable Sampling Method.
2 - An extension of Cluster Random Sampling.
- Draw a sample from a population using smaller and smaller groups (units) at each stage.
3 - Advantages
- Flexibility
- Cost-Effectiveness
4 - Disadvantages
- Subjectivity
- Less Accuracy
5 - Examples
- Study different eating habits in specific regions.
- Research firm (UK); A survey… dividing the country into counties and towns, and randomly selecting clusters from each.
6 - Stages
. Stage 1
Randomly sample clusters (schools).
. Stage 2
Randomly sample individuals from the schools selected.
What is Snowball Sampling? (Types, Definition, Advantages, Disadvantages, Examples, and Note)
1 - Non- Probability Sample.
2 - Have samples that have traits that are rare to find.
3 - Advantages
- Low cost
- Easy to implement
-Researchers can reach a particular population that would otherwise be difficult or impossible to reach.
4 - Disadvantages
- Sampling bias
- Not guaranteed to be a representative of the large population.
5 - Examples
- Exploring secret societies.
- Estimating the size of the problem of trafficking begins.
6 - Note
(Very difficult to collect primary data, unless authorised.)
