Chapter 2

Question 1

What is a population?

Answer 1

The whole set of items that are of interest.

Question 2

What is a census?

Answer 2

A census observes or measures every member of a population.

Question 3

What is a sample?

Answer 3

A selection of observations taken from a sub-set of the population.

Question 4

What is a sample survey?

Answer 4

A sample used to find out information about the population as a whole.

Question 5

Advantages of a census

Answer 5

Should give a completely accurate result.

Question 6

Disadvantages of a census

Answer 6

Time consuming and expensive. Difficult to process information as there is so much of it. Cannot be used when testing to destruction.

Question 7

Advantages of a sample survey.

Answer 7

Costs less and quicker than a census. Fewer people have to respond in the sample. Less data to deal with.

Question 8

Disadvantages of a sample survey.

Answer 8

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

Question 9

What is a random sample?

Answer 9

A sample in which every possible sample of size n has an equal chance of being selected.

Question 10

What is a sampling frame?

Answer 10

A list identifying every single sampling unit that could be included in the sample.

Question 11

What is raw data?

Answer 11

The information obtained from a census or sample survey.

Question 12

When would a census be used?

Answer 12

When the population is very small and extreme accuracy is required.

Question 13

What is unrestricted random sampling?

Answer 13

Random sampling with replacement.

Question 14

What are the advantages of simple random sampling?

Answer 14

Provided that the population is small, it is cheap, simple and standard formulae can be used to analyse the results. Also each person/unit is included only once.

Question 15

What are the disadvantages of simple random sampling?

Answer 15

It is not suitable when the population is large, or when a sampling frame is required.

Question 16

What are two simple techniques for simple random sampling?

Answer 16

Random number sampling and lottery/ticket sampling.

Question 17

What are the advantages of random number sampling?

Answer 17

The numbers are truly random and free from bias, It is easy to use and each number has a known and equal chance of being selected.

Question 18

What is the disadvantage of random number sampling?

Answer 18

Not suitable for large populations.

Question 19

What are the advantages of lottery sampling?

Answer 19

Tickets are drawn at random, it is easy to use and each ticket has a known chance of selection.

Question 20

What are the disadvantages of lottery sampling?

Answer 20

It is not suitable where the population is large and a sampling frame is needed.

Question 21

What is systematic sampling?

Answer 21

The required elements are chosen at regular intervals from an ordered list. Select first unit randomly.

Question 22

How do you calculate a systematic sample?

Answer 22

Take every kth element from a sampling frame where k=N/n N=population size and n=sample size.

Question 23

When is systematic sampling used?

Answer 23

When the population is too large for simple random number sampling.

Question 24

What are the advantages of systematic sampling?

Answer 24

It is simple to use and suitable for large samples.

Question 25

What are the disadvantages of systematic sampling?

Answer 25

It is only random if the ordered list is truly random and it can introduce bias.

Question 26

What is stratified sampling?

Answer 26

A form of random sampling in which the population is divided into mutually exclusive groups (strata) and a random sample is taken from each. The same proportion of each stratum is taken in the sample as is found in the population.

Question 27

How do you calculate the number sampled in a stratum?

Answer 27

It is the number in the stratum divided by the size of the population multiplied by the overall sample size.

Question 28

What are the advantages of stratified sampling?

Answer 28

It can give more accurate estimates than simple random sampling where there are clear strata present and it reflects the population structure.

Question 29

What are the disadvantages of stratified sampling?

Answer 29

Within the strata, the problems are the same as for any simple random sample. If the strata are not clearly defined they may overlap.

Question 30

When is non-random sampling used?

Answer 30

When it is not possible to use random methods, for example when no sampling frame is available.

Question 31

Explain quota sampling.

Answer 31

The population is divided up into groups in terms of gender, social class etc. The number of people in each group is set to try and reflect the group's proportion in the whole population. The interviewer selects the actual sampling units.

Question 32

What are the advantages of quota sampling?

Answer 32

It enables the fieldwork to be done quickly because a representative sample can be achieved with a small sample size. Costs are kept to a minimum. Administering the test is easy.

Question 33

What are the disadvantages of quota sampling?

Answer 33

It is not possible to estimate the sampling errors as it is not a random process. The interviewer has to choose the respondents and may not be able to judge the characteristics easily. Non-responses are not recorded. It can introduce interviewer bias in who is included.

Question 34

What is primary data?

Answer 34

Data which is collected by or on behalf of the person who is going to use it.

Question 35

What is secondary data?

Answer 35

Data which is neither collected by nor on behalf of the person who is going to use it.

Question 36

What are the advantages of primary data?

Answer 36

The collection method is known. The accuracy is known. The exact data needed are collected.

Question 37

What are the disadvantages of primary data?

Answer 37

It is costly in time and effort.

Question 38

What are the advantages of secondary data?

Answer 38

They are cheap to obtain (government publications for example). A large quantity of information is available on the Internet. Much of the data has been collected for years and can be used to plot trends.

Question 39

What are the disadvantages of secondary data?

Answer 39

Bias is not always recognized. It can be in a form that is not easy to deal with.