Sampling

Question 1

Population

Answer 1

The whole set of items that are of interest

Question 2

Sample

Answer 2

Subjection of the population that is of interest

Question 3

Census

Answer 3

Investigation that observes every member of a population

Question 4

Advantages and disadvantages of a census

Answer 4

A:
- should give a completely accurate result

D:
- time consuming and expensive
- large amount of data to process
- can’t be used when testing to destruction

Question 5

Advantages and disadvantages of a sample

Answer 5

A:
- less time consuming and cheaper
- less data to process

D:
- possibly less accurate than census
- if sample is too small, information about subgroups of the population may not be given

Question 6

Factors for sample size

Answer 6

• required accuracy
• available resources
• variation within population

Question 7

Random sampling

Answer 7

Every member of a population has an equal chance of being selected in order to avoid bias

Question 8

Sampling frame

Answer 8

List of every member of the population, each with a unique identifier

Question 9

Method for simple random sampling

Answer 9

1. Create a sampling frame
2. Use a random number generators to generate ‘n’ numbers
3. Select the individuals associated with these numbers to form a sample

Question 10

Method for systematic sampling

Answer 10

1. Create a sampling frame
2. Calculate the ‘sampling interval’ = N/n
3. Select at random a starting point
4. Select all other sample remembers at a regular interval

Question 11

Method for stratified sampling

Answer 11

1. Build a sampling frame
2. Split the population into mutually exclusive groups (strata)
3. Take simple random sample from each group where the number selected from each group equals (number in that group/ total population) x overall sample size

Question 12

Advantages and disadvantages of simple random sampling

Answer 12

A:
- easy and cheap for small populations and samples
- each sampling unit has an equal chance of being selected :. Mostly free of bias

D:
- not suitable for large populations and samples
- requires a sampling frame

Question 13

Advantages and disadvantages of systematic sampling

Answer 13

A:
- simple and quick to use
- suitable for large populations and samples

D:
- requires a sampling frame
- can introduce bias if sampling frame is not random

Question 14

Advantages and disadvantages of stratified sampling

Answer 14

A:
- sample accurately reflects population structure
- guarantees proportional representation of groups within a population

D:
- need to split the population into sub groups which can be time consuming

Question 15

Method for quota sampling

Answer 15

1. The population is divided into groups according to a certain characteristic
2. An interviewer meets people and asses their group
3. After interview the interviewer allocates them to the appropriate quota until all quota are filled

Question 16

Opportunity sampling

Answer 16

Sample is obtained from the people available at the time of study who fit the chosen criteria

Question 17

Advantages and disadvantages of quota

Answer 17

A:
- no sampling frame is required
- representative of the population

D:
- non-random so could introduce bias
- highly dependent on individual researcher
- population must be split into groups which can be time consuming
- non-responses are not recorded

Question 18

Advantages and disadvantages of opportunity sampling

Answer 18

A:
- quick, easy, and cheap
- no sampling frame is required

D:
- unlikely to produce a representative sample
- non-random sampling can introduce bias
- highly dependent on individual researcher