Statistics (Unit 1) - Data Collection Flashcards
What is a census?
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.
Adv of a Census
It should give completely accurate result.
Adv of a Sample
- Less time consuming and expensive than a census
- Fewer people have to respond
- Less data to process than in a census
Dis of a Census
- Time consuming/expensive
- Hard to process large quantities of data
Dis of a Sample
- The data may not be as accurate
- Sample may not be large enough to give enough info about smaller groups of the population
Simple random sampling
Where every sample has an equal but random chance of being selected
Systematic sampling
Required elements are chosen at regular intervals from an ordered list
Stratified sampling
The population is divided into mutually exclusive strata and a random sample is taken from each
Adv of Simple random sampling
- Free of bias
- Easy and cheap for small samples
- Each unit has equal
chance of being selected
Adv of Systematic sampling
- Simple and quick
- Suitable for large samples
Adv of stratified sampling
- Accurately reflects population structure
- Shows proportional representation of groups in a population
Dis of simple random sampling
- Not suitable for large sizes
- Sampling frame is needed
Dis of systematic sampling
- Sampling frame needed
- Can introduce bias if frame is not random
Dis of Stratified sampling
- Population must be clearly classified into distinct strata
- Selection in each stratum suffers from same Dis as simple random sampling
Quota sampling
An interviewer/researcher selects a sample that reflects the characteristics of the whole population
Opportunity sampling
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
Adv of Quota sampling
- Allows small samples to be representative of the population
- No sampling frame
- Quick, easy, inexpensive
- Easy comparison between different groups
Adv of Opportunity sampling
- Easy to do
- Inexpensive
Dis of Quota sampling
- Non random, can induce bias
- Population is divided into groups which can be costly/inaccurate
- More groups mean more time and expense
- Non-responses not recorded
Dis of Opportunity sampling
- Unlikely to provide representative sample
- Highly dependant of individual researcher
Quantitative data
Data associated with numerical observations
Qualitative data
Data associated with non-numerical observations
Continuous data
Data that can take any value in a given range
Discrete data
Data that can take only specific values in a given range
