What is a population?
The whole set of items that are of interest to you that you wish to sample
What is a census?
A measure of every member of a population
What is a sample?
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
What is a sampling unit?
Individual units of a population
What is a sampling frame?
Sampling units which are numbered to form a list
What is an advantage of a census?
It will give a completely accurate result as you are questioning everyone
What is are 3 disadvantages of a census?
- Time Consuming
- Expensive
- Cannot be used when the testing involves destroying the items
What are 3 advantages of a sample?
- Less time consuming and expensive than a census
- Fewer people have to respond
- Less data to be processed than a census
What are 2 disadvantages of a census?
- The data may not be accurate
- The sample may not be large enough to give information about small subgroups of the population
What is a simple random sample?
Where every size of n has an equal chance of being selected
What is systematic sampling?
The elements are chosen at regular intervals eg every 5th person is chosen
What is stratified sampling?
The population is divided into mutually exclusive strata and a sample is taken from each eg they are split into males and females and then 20 people from each is taken
What are 3 advantages of simple random sampling?
- Free of bias
- Easy and cheap to use for small samples
- Each sample unit has an equal chance of being selected
What are 2 disadvantages of simple random sampling?
- Not suitable when the population size is large as it may be time consuming and expensive
- A sampling frame is needed
What are 2 advantages of systematic sampling?
- Simple and quick to use
- Suitable for large samples ad populations
What are 2 disadvantages of systematic sampling?
- A sampling frame is needed
- It can introduce bias if the sampling frame is not random
What are 2 advantages of stratified sampling?
- Sample accurately reflects the population structure
- Guarantees accurate representation of groups in a population
What are 2 disadvantages of stratified sampling?
- Population must be clearly classified into a distinct strata
- Selection within each stratum suffers from the same disadvantages as simple random sampling
What are the 2 types of non-random sampling?
- Quota sampling
- Opportunity sampling
What is quota sampling?
An interviewer selects a sample that reflects the characteristics of the whole population eg they will look for people aged 21-30, 30-40 and then ask them the question
What is opportunity sampling?
Taking a sample from people who are available at the time the study is carried out eg you stand outside a supermarket and ask people to take your survey
What are 4 advantages of quota sampling?
- Allows a small sample size to still be representative of the population
- No sampling frame required
- Quick, easy and inexpensive
- Allows for easy comparison between different groups
What are 4 disadvantages of quota sampling?
- Non-random sampling can introduce
- Population must be divided into groups which can be costly and inaccurate
- Increasing scope of study increases number of groups which adds time and expense
- Non-responses are not recorded as such
What are 2 advantages of opportunity sampling?
- Easy to carry out
- Inexpensive
