Year 1 Chapter 1 Flashcards
What is a population
The whole set of items that are of interest.
What is a census
Observes or measures 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 are advantages of a census
It should give a completely accurate result
What are advantages of a sample
Less time consuming & expensive than a census
Fewer people have to respond
Less data to process than in a census
What are disadvantages of census
Time consuming & expensive
Cannot be used when the testing process destroys the item
Hard to process large quantity of data
What are disadvantages of sample
Data might not be as accurate
Sample may not be large enough to give information about small subunit groups of the population
What is a sampling unit
Individual units of a population
What is a sampling frame
Sampling units of a population are individually named or numbered to form a list
What are 3 methods of random sampling
Simple
Systematic
Stratified
What is a simple random sample
Size n
Where every sample of size n has an equal chance of being selected
What is lottery sampling
The members of sampling frame could be written on tickets and placed into a ‘hat’
Required number of tickets are drawn out
What are 2 method of choosing numbers randomly
Random number generator
Lottery sampling
What is systematic sampling
Required elements are chosen at regular intervals from an ordered list
E.g.
sample size 20 required from population of 100
Do 100/20=5 so take every 5th person
What is a stratified sample
Population divided into mutually exclusive strata and a random sample is taken from each.
Equation to work out the number sampled in a stratum
Number in stratum
——————————— x overall sample size
Number in population
What are advantages of simple random sampling
Free of bias
Easy & cheap to implement for small populations and small samples
Each sampling unit has a known and equal chance of selection
What are disadvantages of simple random sampling
Not suitable when population size / sample size is larger as its potentially time consuming, disruptive and expensive
Sampling frame is needed
Advantages of systematic sampling
Simple and quick to use
Suitable for larger samples and large populations
Disadvantages of systematic sampling
Sampling frame needed
Can introduce bias if sampling frame isn’t random
Advantages of stratified sampling
Sample accurately reflects population structure
Guarantees proportional representation of groups within a population
Disadvantages of stratified sampling
Population must be clearly classified into distinct strata
Selection within each stratum suffers from same disadvantages as simple random sampling
What are 2 types of non-random sampling
Quota
Oppurtunity
What is quota sampling
Interviewer/researcher selects a sample that reflects characteristics of the whole population
