AS Statistics Flashcards
(40 cards)
Define population
the whole set of items that are of interest
What is a census?
A census observes or measure 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
Name the advantages of a census
It should give a completely accurate result
Name the disadvantages of a census
- Time consuming and expensive
- Hard to process large quantity of data
Name the advantages of a sample
- Less time consuming and expensive than census
- Fewer people have to respond
- Less data to process than in a census
Name the disadvantages of a sample
- Data may not be as accurate
- Sample may not be large enough to give info bout the whole population
What are sampling units?
Individual units of a population
What is a sampling fram?
Sampling units named or numbered to form a list
What are the 3 methods of random sampling?
- Simple random sampling
- Systematic sampling
- Stratified sampling
What is meant by simple random sampling?
Every sample has an equal chance of being selected
What is meant by systematic sampling?
The required elements are chosen at regular intervals from an ordered list
What is meant by stratified sampling?
The population is divided into mutually exclusive strata and a random sample is taken from each
Stratified sampling formula
Number in stratum/number in population X overall sample size
Name the advantages of simple random sampling
- Free of bias
- Easy and cheap to implement for small populations
- Each sampling unit has a known and equal chance of selection
Name the disadvantages of simple random sampling
- Not suitable when the population size or sample size is large
- A sampling frame is needed
Name the advantages of systematic sampling
- Simple and quick to use
- Suitable for large samples and large populations
Name the disadvantages of systematic sampling
- A sampling frame is needed
- Can introduce bias if sampling frame is not random
Name the advantages of stratified sampling
- Sample accurately reflects the population structure
- Guarantees proportional representation of groups within a population
Name the disadvantages of stratified sampling
- Population must be clearly classified into distinct strata
What are the two types of non-random sampling?
1.Quota sampling
2. Opportunity sampling
What happens in quota sampling?
An interviewer or researcher selects a sample that reflects the characteristics of the whole population
What happens in opportunity (convenience) sampling?
Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for
Name the advantages of quota sampling
- Allows a small sample to still be representative of the population
- No sampling frame required
- Quick, easy and inexpensive
- Allows for comparison between different groups within a population
