What is a population?
A complete group of items for which information is required
What is consensus ?
The process of fully surveying a population
What is a sample ?
A subset of the population
How do we collect data ?
By statistical inference = reliable conclusions can only be made from samples that are representative of the population
What is representative sample ??
A sample that is similar to the population on all characteristics, except that it includes fewer people
What is a sampling frame ?
A complete list of potential items from which we draw items to be included in the sample
What are probability samples ?
When each element of the population has a known probability of being included in the sample
What is simple random sampling ?
Simple random sampling is obtained is each element in the population, not already in the sample, has an equal chance of being taken up into the sample on the next draw
What is the method of simple random sampling ?
- List of all population elements, numbered
- Use a mechanical method to select the sample elements
- Use the table of random numbers (Table AI)
- Make use of the computer (random number generator)
What is stratified sampling ?
When the population is divided into a number of natural, non-overlapping groups/strategy that are more or less homogenous
- elements are randomly selected from each group
- the number from each stratum is proportional to the population
- number of sample elective from each group may be different
- If this number of elements is proportional to the stratum size, the sample is called a proportionally stratified sample
What is the stratified sampling method?
- 1st divide your population into males and females if you are using gender as your stratification variable
- Take a random samples from each group
- put those two sets together and you now have your final sample
- obtaining a sample with no or very few males/females is possible
What is cluster sampling ?
When the population elements are naturally grouped together yo form so-called clusters where each cluster consists of a group of heterogenous elements
What is the method of cluster sampling ?
- A number if clusters is randomly chosen
- All the elements from the chosen clusters are incorporated in the sample (one-stage cluster sampling)
OR
elements are randomly selected from the chosen clusters to be included in the sample (two-stage cluster sampling)
What are the samples under Non-probability samples ?
- convenience sample
- judgement sample
- Quota sample
What is a convenience sample ?
When a sample which is convenient for the researcher is taken and does not necessarily represent a population
- units are selected which are easily attainable and readily available
What are judgement samples?
When samples are taken to include the “best” sample elements in the sample according to the researchers judgement
What is a Quota sample ?
The non-probability equivalent of stratified sampling
- the population is divided into segments and a Quota element from each segment is included in the sample
- Quotas are sometimes based on proportions of populations, but the choice of sample elements is made according to a non-probability method (convenience or judgement)
What do we have under errors and bias in sampling ?
- sample error
- sampling bias
- sampling observation errors
What is sample error ?
A reflection of the inherent inability of the sample to provide completely accurate information about a population
- it is inherent to an sample, it cannot be avoided
- can bring decreased by taking a larger sample
What is sampling bias ?
Sampling bias occurs when certain sections of the population are represented to a lesser degree or not represented at all
What ade sampling observation errors ?
Errors incurred during the collection of data
- faulty or inaccurate measuring instruments, unreliability of the surveyor or respondent
What are the responsibilities under errors and bias in sampling ?
- honesty when working with data
- anonymity vs confidentiality
- ethics are important when working with people
- Non-probability sampling methods are subjective
