Sampling

Question 1

What is a population?

Answer 1

The whole set of/all items that are of interest

Question 2

What is a census?

Answer 2

An observation of all/every member of the population

Question 3

2

What is a sample?

Answer 3

• A selection of observations taken from a subset of the population
• Used to find out information about the population as a whole

Question 4

1

List the advantages of a census

Answer 4

• Should give completely accurate result

Question 5

4

List the disadvantages of a census

Answer 5

• Time consuming and expensive
• Cannot be used when testing process destroys the item
• Hard to process large quantities of data
• Hard to get everyone to respond

Question 6

3

List the advantages of a sample

Answer 6

• Less time consuming and expensive than a census
• Fewer people have to respond
• Less data to process than in a census

Question 7

3

List the disadvantages of a sample

Answer 7

• Data may not be as accurate
• Sample may not be large enough to give information about small sub-groups of the population
• Possible bias

Question 8

What is a sampling frame?

Answer 8

An ordered list of the sampling units of the population

Question 9

What are sampling unit?

Answer 9

Individual units of a population

Question 10

What is a common way to improve a sample?

Answer 10

Test a larger number of (avacados)

Question 11

1

What do all random sampling methods require

Answer 11

A sampling frame

Question 12

What is simple random sampling?

Answer 12

sampling where every sample of size n has an equal and known chance of selection

Question 13

2

What are techniques for simple random sampling?

Answer 13

• Generate a number: random number generator, random number table
• Lottery sampling: tickets picked from a hat

Question 14

What is systematic sampling?

Answer 14

Sampling where the required elements are chosen at regular intervals from an ordered list

Question 15

2

What is stratisfied sampling?

Answer 15

• Population is divided into mutually exclusive strata/groups (e.g. males and females)
• A random sample is taken from each

Question 16

3

List the advantages of simple random sampling

Answer 16

• Free of bias
• Easy and cheap to implement for small populations and small samples
• Each sampling unit has a known and equal chance of selection

Question 17

2

List the disadvantages of simple random sampling

Answer 17

• Not suitable when the population or sample size is large
• A sampling frame is needed

Question 18

2

List advantages of systematic sampling

Answer 18

• Simple and quick to use
• Suitable for large samples and large populations

Question 19

2

List disadvantages of systematic sampling

Answer 19

• A sampling frame is needed
• It can introduce bias if the sampling frame is not random

Question 20

2

List advantages of stratisfied sampling

Answer 20

• Sample accurately reflects population structure
• Guarantees PR of groups within population

Question 21

2

List disadvantages of stratisfied sampling

Answer 21

• Population must be clearly classified into distinct strata
• Selection within each stratum suffers from the same disadvantages as simple random sampling

Question 22

3

List common general errors in sampling

Answer 22

• Error in sampling frame
• Some data is erroneous
• Natural variance (due to small sample or different samples lead to different results)

Question 23

What is quota sampling?

Answer 23

An interviewer/researcher selects a sample that reflects the characteristics of the population as a whole (interviewer selects actual sampling)

Question 24

2

What should be done once quota sampling has begun

Answer 24

• Continue collecting data/info until all quotas are full
• If quota full, further responses should be ignored

Question 25

# 2 What is opportunity sampling?

Answer 25

Taking sample from people who: 1. are available at the time of the study 2. who fit the criteria you are looking for (eg. elderly people)

Question 26

# 4 List the advantages of quota sampling

Answer 26

* Allows a small sample to be representative of the population * No sampling frame required (interviewer selects sample) * Quick, easy and inexpensive * Allows for easy comparison between different groups within a population

Question 27

# 4 List the disadvantages of quota sampling

Answer 27

* Non-random sampling can introduce bias * Population must be divided into groups which can be costly or innacurate * Increasing scope of study increases number of groups, which adds time and expense * Non-responses are recorded as such

Question 28

# 2 List the advantages of opportunity sampling

Answer 28

* Easy to carry out * Inexpensive

Question 29

# 2 List the disadvantages of opportunity sampling

Answer 29

* Unlikely to produce representative sample * Highly dependent on individual researcher (bias)

Question 30

Variables associated with numerical observations are called (...) data/variables

Answer 30

quantitative

Question 31

Variables associated with non-numberical observations are called (...) data/variables

Answer 31

qualitative

Question 32

A variable that can take any value in a given range is a (...) variable

Answer 32

continuous

Question 33

A variable that can take only specific values in a given range is a (...) variable

Answer 33

discrete