AS Statistics: 1 Data Collection

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 measure of every member of a population.

Question 3

What is a sample?

Answer 3

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

• Time-consuming and expensive.
• Cannot be used when the testing process destroys the item.
• Hard to process a large quantity of data.

Question 6

What are 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 a census.

Question 7

What are the disadvantages of a sample?

Answer 7

• The data may not be as accurate.

- The sample may not be large enough to give information about small sub-groups of the population.

Question 8

What are sampling units?

Answer 8

Individual units of a population.

Question 9

What is a sampling frame?

Answer 9

When sampling units are individually named or numbered to form a list.

Question 10

What is simple random sampling?

Answer 10

Where every sample has an equal chance of being selected.

Question 11

What are the advantages of simple random sampling?

Answer 11

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

Question 12

What are the disadvantages of simple random sampling?

Answer 12

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

Question 13

What is systematic sampling?

Answer 13

When elements are chosen at regular intervals from an ordered list.

Question 14

What are the advantages of systematic sampling?

Answer 14

• Simple and quick to use.

- Suitable for large samples and large populations.

Question 15

What are the disadvantages of systematic sampling?

Answer 15

• A sampling frame is needed.

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

Question 16

What is stratified sampling?

Answer 16

When the population is divided into mutually exclusive strata (e.g. males and females) and a random sample is taken from each.

Question 17

What are the advantages of stratified sampling?

Answer 17

• Sample accurately reflects the population structure.

- Guarantees proportional representation of groups within a population.

Question 18

What are the disadvantages of stratified sampling?

Answer 18

• Population must be clearly classified into distinct strata

- Selection within each stratum suffers from the same disadvantages as simple random sampling.

Question 19

What is quota sampling?

Answer 19

An interviewer or researcher selects a sample that reflects the characteristics of the whole population.

Question 20

What are the advantages of quota sampling?

Answer 20

• 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 21

What are the disadvantages of quota sampling?

Answer 21

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

Question 22

What is opportunity sampling?

Answer 22

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.

Sometimes called convenience sampling.

Question 23

What are the advantages of opportunity sampling?

Answer 23

• Easy to carry out.

- Inexpensive.

Question 24

What are the disadvantages of opportunity sampling?

Answer 24

• Unlikely to provide a representative sample.

- Highly dependent on individual researcher.

Question 25

What are quantitative variables/data?

Answer 25

Variables/data associated with numerical observations.

Question 26

What are qualitative variables/data?

Answer 26

Variables/data associated with non-numerical observations.

Question 27

What are continuous variables?

Answer 27

Variables that can take any value in a given range.

Question 28

What are discrete variables?

Answer 28

Variables that can take only specific values in a given range.

Question 29

What can we tell from classes in frequency tables?

Answer 29

• Class boundaries tell you the max and min values that belong to each class.
• The midpoint is the average of the class boundaries.
• The class width is the difference between the upper and lower class boundaries.

Question 30

What does the large data set show?

Answer 30

Consist of weather data samples provided by the Met Office for 5 UK weather stations and 3 overseas over 2 time periods.

Question 31

What were the time periods of the large data set?

Answer 31

May - Oct 1987.

May - Oct 2015.

Question 32

Where were the large data set samples taken?

Answer 32

• Leuchars.
• Leeming.
• Heathrow.
• Hurn.
• Camborne.
• Jacksonville.
• Perth.
• Bejing.

Question 33

What variables were measured as part of the large data set in the UK?

Answer 33

• Daily mean temperature (ᵒC).
• Daily total rainfall (mm).
• Daily total sunshine.
• Daily mean wind direction and wind speed (in knots: 1kn = 1.15mph) (also categorized according to the Beaufort scale).
• Daily maximum gust (kn).
• Daily maximum relative humidity (%).
• Daily mean cloud cover (oktas).
• Daily mean visibility (Dm).
• Daily mean pressure (hPa).

Question 34

What variables were measured as part of the large data set overseas?

Answer 34

• Daily mean temperature (ᵒC).
• Daily total rainfall (mm).
• Daily mean pressure (hPa).
• Daily mean windspeed.