Sampling

Question 1

What are the advantages of a census

Answer 1

completely accurate result

Question 2

Disadvantages of a census

Answer 2

• time consuming
• expensive
• large amount of data to process
• cannot be used when testing involves destruction

Question 3

What is a sampling frame

Answer 3

a list of all the members of the sample

Question 4

What are the advantages of random sampling

Answer 4

• random and free from bias
• easy to use
• each number has equal chance of selection

Question 5

How do you carry out random sampling

Answer 5

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

Question 6

Disadvantages of random sampling

Answer 6

Not suitable when population size is large

Question 7

How do you carry out Lottery Sampling

Answer 7

Each element of population is identified by some characteristic on a ticket. Tickets are drawn randomly from a container (without replacement)

Question 8

Advantages of lottery sampling

Answer 8

• tickets drawn at random
• easy to use
• each ticket has an equal chance of selection

Question 9

Disadvantages lottery sampling

Answer 9

• not suitable when population size is large
• a sampling frame is needed

Question 10

How do you carry out Systematic Sampling

Answer 10

• Required elements are chosen at regular intervals in an ordered list
• every kth element is taken
  -k = population size/sample size

Question 11

Advantages systematic sampling

Answer 11

• simple
• suitable for large samples

Question 12

Disadvantages systematic sampling

Answer 12

• only random is ordered list is truly random, so can introduce bias

Question 13

How do you carry out Stratified Sampling

Answer 13

• 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

Question 14

Advantages stratified sampling

Answer 14

• can give more accurate estimates than simple random sampling where there are clear strata present
• reflects population structure

Question 15

Disadvantages stratified sampling

Answer 15

• w/in strata problems are same as for random samples
• if strata not clearly defined, may overlap

Question 16

How is quota sampling done

Answer 16

• 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

Question 17

Advantages of Quota sampling

Answer 17

• enables fieldwork to be done quickly because a representative sample can be achieved with a small sample size
• cheap
• administering test is easy

Question 18

Disadvantages of Quota sampling

Answer 18

• 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

Question 19

What kind of sampling is often used in market research

Answer 19

Cluster sampling

Question 20

How do you carry out cluster sampling

Answer 20

• 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

Question 21

Advantages cluster sampling

Answer 21

• unbiased when clusters approx same size
• cheaper, can increase sample size
• each cluster represents entire population, so more subjects can be included in study

Question 22

Disadvantages cluster sampling

Answer 22

• 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