Chapter 1: Data Collection

Question 1

What is a population?

Answer 1

A population is the whole set of items that are of interest.

Question 2

What is the purpose of a census?

Answer 2

A census observed or measures every member of a population.

Question 3

What is a sample?

Answer 3

A sample is a selection of observations taken from a subset of the population which is used to find out information about the population as a whole.

Question 4

What are the advantages of a census?

Answer 4

It should give a completely accurate result.

Question 5

What are the disadvantages of a census?

Answer 5

A census is time consuming and expensive, cannot be used when the testing process destroys the item; and produces a large quantity of data.

Question 6

What are the advantages of a sample?

Answer 6

A sample is less time consuming and expensive than a census, fewer people have to respond, and there is less data to process.

Question 7

What are the disadvantages of a sample?

Answer 7

In a sample, the data may not be as accurate. Also, the sample may not be large enough to give information about small sub-groups of the population.

Question 8

How does sample size correlate to variation in a population?

Answer 8

If a population is very varied, you need a larges sample than if the population were uniform.

Question 9

What are sampling units?

Answer 9

Individual units of a population are known as sampling units.

Question 10

What is a sampling frame?

Answer 10

Sampling units of a population are often individually named or numbered to form a list called a sampling frame.

Question 11

What are the three methods of random sampling?

Answer 11

Simple random sampling, systematic sampling, and stratified sampling.

Question 12

What is a simple random sample?

Answer 12

A simple random sample of size n is one where every sample of size n has an equal chance of being selected.

Question 13

How is a simple random sample carried out?

Answer 13

First, you need a sampling frame. Each person or thing is allocated a unique number and a selection of these numbers is chosen at random by generating random numbers or lottery sampling.

Question 14

What is systematic sampling?

Answer 14

In systematic sampling, the required elements are chosen at regular intervals from an ordered list. The first person in a systematic sample is chosen at random.

Question 15

What is stratified sampling?

Answer 15

In stratified sampling, the population is divided into mutually exclusive strata and a random sample is taken from each. The proportion of each strata sampled should be the same.

Question 16

How can the number of people sampled in a stratum be determined?

Answer 16

[(number in stratum) ÷ (number in population)] x overall sample size

Question 17

What are the advantages of simple random sampling?

Answer 17

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

Question 18

What are the disadvantages of simple random sampling?

Answer 18

• Not suitable for large population or sample size

- A sampling frame is needed

Question 19

What are the advantages of systematic sampling?

Answer 19

• Simple and quick to use

- Suitable for large samples/populations

Question 20

What are the disadvantages of systematic sampling?

Answer 20

• A sampling frame is needed

- It can introduce bias if the sampling frame is not random

Question 21

What are the advantages of stratified sampling?

Answer 21

• Sampling accurately reflects the population structure

- Guarantees proportional representation of groups within a population.

Question 22

What are the disadvantages of stratified sampling?

Answer 22

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

Question 23

What are the types of non-random sampling?

Answer 23

Quota sampling and opportunity sampling.

Question 24

What is quota sampling?

Answer 24

In quota sampling, an interviewer or researcher selects a sample that reflects the characteristics of the whole population.

Question 25

How is quota sampling carried out?

Answer 25

The population is divided into groups according to a given characteristic. The size of each group determines the proportion of the sample that should have that characteristic.

As an interviewer, you would meet people, assess their group and then, after interview, allocate them into the appropriate quota.

This continues until all quotas have been filled. If a person refuses to be interviewed or the quota into which they fit is full, then you simply ignore them and move on to the next person.

Question 26

What is opportunity sampling?

Answer 26

Opportunity sampling consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Question 27

What are the advantages of quota sampling?

Answer 27

• Allows a small sample to still be representative of the population
• No sampling frame required
• Quick, easy and inexpensive
• Allows for easy comparison between different groups within a population

Question 28

What are the disadvantages of quota sampling?

Answer 28

• Non-random sampling can introduce bias
• Population must be divided into groups, which can be costly or inaccurate
• Increasing scope of study increases number of groups, which adds time and expense
• Non-responses are not recorded as such

Question 29

What are the advantages of opportunity sampling?

Answer 29

• Easy to carry out

- Inexpensive

Question 30

What are the disadvantages of opportunity sampling?

Answer 30

• Unlikely to provide a representative sample

- Highly dependent on individual researcher

Question 31

What is a continuous variable?

Answer 31

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

Question 32

What is a discrete variable?

Answer 32

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

Question 33

Give, from South to North, the five UK weather stations in the large data set.

Answer 33

Camborne, Hurn, Heathrow, Leeming and Leuchars

Question 34

Which overseas stations are in which hemisphere?

Answer 34

Perth is in the southern hemisphere. Beijing and Jacksonville is in the northern hemisphere.