What are the advantages of a census
completely accurate result
Disadvantages of a census
- time consuming
- expensive
- large amount of data to process
- cannot be used when testing involves destruction
What is a sampling frame
a list of all the members of the sample
What are the advantages of random sampling
- random and free from bias
- easy to use
- each number has equal chance of selection
How do you carry out random sampling
Assign each element of the sampling frame a number, and use the random number function on a calculator to select the sample, ignoring repeats or too large numbers
Disadvantages of random sampling
Not suitable when population size is large
How do you carry out Lottery Sampling
Each element of population is identified by some characteristic on a ticket. Tickets are drawn randomly from a container (without replacement)
Advantages of lottery sampling
- tickets drawn at random
- easy to use
- each ticket has an equal chance of selection
Disadvantages lottery sampling
- not suitable when population size is large
- a sampling frame is needed
How do you carry out Systematic Sampling
- Required elements are chosen at regular intervals in an ordered list
- every kth element is taken
-k = population size/sample size
Advantages systematic sampling
- simple
- suitable for large samples
Disadvantages systematic sampling
- only random is ordered list is truly random, so can introduce bias
How do you carry out Stratified Sampling
- Population divided into groups (strata) and simple random sample is carried out in each group
- same proportion is sampled from each star using sample size/population size
Advantages stratified sampling
- can give more accurate estimates than simple random sampling where there are clear strata present
- reflects population structure
Disadvantages stratified sampling
- w/in strata problems are same as for random samples
- if strata not clearly defined, may overlap
How is quota sampling done
- population divided into groups (in terms gender, social class, etc.)
- quota of people in each group is set to try select groups proportion in whole population
- interviewer selects actual sampling units
Advantages of Quota sampling
- enables fieldwork to be done quickly because a representative sample can be achieved with a small sample size
- cheap
- administering test is easy
Disadvantages of Quota sampling
- not possible to estimate sampling errors as not random
- non-responses are not recorded
- can introduce bias in who is included
- Interviewers may not be able to judge the characteristics easily
What kind of sampling is often used in market research
Cluster sampling
How do you carry out cluster sampling
- population divided into separate groups (clusters)
- each cluster treated as sampling units and random sample of clusters is selected
- elements of these clusters are then sampled
Advantages cluster sampling
- unbiased when clusters approx same size
- cheaper, can increase sample size
- each cluster represents entire population, so more subjects can be included in study
Disadvantages cluster sampling
- Prone to bias, if clusters formed under biased option then inferences abt whole population are biased as well
- prone to higher sampling error due to limited clusters being incl in sample, leaving a significant proportion of the population unsampled
