Population
A whole set of items that are of interest
Census
Observes or measures everyone in the population
Sample
A subset of the population that is used to gather information about the whole population
Simple random sampling
Every member of the population has an equal chance of being chosen
Systematic sampling
Elements are chosen at regular intervals from an ordered list
Stratified sampling
Population is divided into different strata and a random sample is taken from each
Formula for stratified sampling
(no in a stratum/no in population) x overall sample size
Quota sampling
A researcher selects a sample the reflects the characteristics of the whole population
Opportunity sampling
Taking the sample from people who are available at the time the study is happening who also fit the criteria.
Advantages of a census
It should give a completely accurate result
Disads of a census
- Time consuming/expensive
- Hard to process large quantities of data
- Can’t be used when the testing process destroys the item
Advantages of sampling
- Less time consuming/expensive
. Less data to process - Less people have to respond
Disads of samples
- Data may not be accurate
- Sample may not be big enough to give info about everyone
Ads of simple random sampling
- Free of bias
- Easy and cheap to do for small samples/pop.
- Each sampling unit has an equal chance of selection
Disads of SRS
- Not good for large populations/samples bc it’s time consuming/expensive otherwise
- A sampling frame is needed
Advantages of Systematic sampling
- Simple/quick
- Good for big samples/pop.
Disads of systematic sampling
- needs sampling frame
- It could into. bias if frame isn’t random
Ads of Strat.
- Accurately represents population structure
- Guarantees PR of groups in a populations.
Disads of Strat
- Pop. has to be clearly classified into distinct groups
- Within each group, the disadvanatge is == to SRS disads..
Ads of quota sampling
- Allows a small sample to be rep. of pop.
- No frame needed
- Quick, easy, cheap
- Allows for easy comparison between diff groups in a pop.
Disads of quota sampling
- non-random sampling can give bias
- Population has to be split into groups which can be $$$
- Increasing the scope of study increases no. of groups- time waste
Advantages of opportunity sampling
- Easy to do
- Cheap
Disads of opportunity sampling
- Not gonna give a representative sample
- Highly dependent on person who does the sample
Discrete data
Fixed data e.g the amount of people in a room – you cannot have 2.65 people in a room
