Data Collection Flashcards
What is a population?
A whole set of items of interest
What is a Sampling Frame?
individually named/numbered sampling units to form a list of the population
What are Sampling Units?
individual units of a population
What does a census do?
It observes or measures every member of a population
What is an advantage of a census?
- completely accurate and representative of the whole population
What are 3 disadvantages of the census?
- is time consuming and costly
- cannot be used if testing destroys the items
- the large amount of data can be hard to process
What is a sample?
A selection of observations from a subset of a population
What are 3 advantages of sampling?
- Less time consuming and expensive than census
- fewer people need to respond
- less data to process
What are 2 disadvantages of sampling?
- might not be as accurate
- sample too small = no info about small sub-groups
What is random sampling?
every member of the population has equal change of selection (should be representative and lower bias)
What is simple random sampling?
Every one has an equal chance of selection
How do you carry out simple random sampling?
- Get a sampling frame
- a) use a random number generate to select random numbered items
b) lottery sampling, put on paper and in a hat
What are 3 advantages to simple random sampling?
- no bias
- its easy and cheap
- each unit has an equal and known change of selection
What are 2 disadvantages to simple random sampling?
- when the population is large, it increases time, disruption and cost
- a sampling frame is needed
What is systematic sampling?
elements are chosen at regular intervals from a list
How is systematic sampling carried out?
population/sample size gives you the interval required, a person from within the first interval is chosen at random, from that person onwards the person of that interval is chosen
What is 2 advantages of systematic sampling?
- simple and quick
- suitable for large samples and populations
What are 2 disadvantages of systematic sampling?
- sampling frame needed
- can be bias if the frame isnt random
What is stratified sampling?
population divided into strata, a random sample is taken from each
How is stratified sampling carried out?
the proportion of people in each strata is the same as the groups’ proportion of the population - number sampled in a strata = number in stratum/number in population * overall sample size - then simple random or systematic sampling used within groups
What are 2 advantages of stratified sampling?
- Accurately represents the population structure
- guarantees proportional representation of groups
What is quota sampling?
a sample of people is selected, representative of the whole population
How is quota sampling carried out?
Population is divided into groups according to a characteristic (proportional to the size of the groups) - people met and assed into groups - repats until quotas full (if quota full or person ignores - move on)
What are 4 advantages of quota sampling?
- a small sample that is still representative is used
- no sampling frame
- quick, easy and inexpensive
- allows for easy comparisons between groups
What are 4 disadvantages of quota sampling?
- can introduce bias
- population must be divided into groups
- increasing scope of study means, increasing groups, increasing time and cost
- people who don’t respond or in already filled quotas aren’t recorded
What is opportunity sampling?
Taking a sample of people available at time of study and that fit the criteria
What are 2 advantages of opportunity sampling?
- easy to carry out
- inexpensive
What are 2 disadvantages of opportunity sampling?
- unlikely to be representative
- dependant on the individual researcher
