Statistics - Module 1

Question 1

Def of population

Answer 1

The whole set of items that are of interest

Question 2

Def of census

Answer 2

Observes or measures every member of a population

Question 3

Sample def

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

Advantages of a census

Answer 4

Should give a completely accurate result

Question 5

Disadvantages of a census

Answer 5

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

Question 6

Advantages of samples

Answer 6

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

Question 7

Disadvantages of sampling

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

Sampling units of a population that are individually named or numbered to form a list

Question 10

What are the three methods of random sampling?

Answer 10

Simple random sampling
Systematic sampling
Stratified sampling

Question 11

What is simple random sampling?

Answer 11

When the sample of size ‘n’ is one where every sample of size ‘n’ has an equal chance of being selected

Question 12

Process for random sampling

Answer 12

Acquire a sample frame - usually a list of people or things
Allocate each person or thing a unique number
Choose a number at random either by a random number generator or lottery sampling

Question 13

What is lottery sampling?

Answer 13

The members of the sampling frame could be written on tickets and placed into a ‘hat’.
The required number of tickets would then be drawn out.

Question 14

What is systematic sampling?

Answer 14

When the required elements are chosen at regular intervals from an ordered list.
E.g. for a sample of 20 from population 100,
You would take every fifth person, since 100/20 = 5
The first person to be chosen should be chosen at random, e.g. 2, 7, 12, etc.

Question 15

What is stratified sampling?

Answer 15

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

Question 16

Process of stratified sampling

Answer 16

Proportion of each strata sampled should be the same.
You can use a formula to calculate the number of people you should sample from each stratum:
No. in stratum/no. in population x overall sample size

Question 17

Advantages of simple random sampling

Answer 17

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 18

Disadvantages of simple random sampling

Answer 18

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

Question 19

Advantages of systematic sampling

Answer 19

Simple and quick to use

Suitable for large samples and large populations

Question 20

Disadvantages of systematic sampling

Answer 20

A sampling frame is needed

It can introduce bias if the sampling frame is not random

Question 21

Advantages of stratified sampling

Answer 21

Sample accurately reflects the population structure

Guarantees proportional representation of groups within a population

Question 22

Disadvantages of stratified sampling

Answer 22

Population must be clearly classified into distinct strata
Selection within each stratum suffers from the same disadvantages as simple random sampling
- need to establish a sampling frame
- if sample size not large enough, can be inaccurate

Question 23

Two types of non-random sampling

Answer 23

Quota sampling

Opportunity sampling

Question 24

What is quota sampling?

Answer 24

Where an interviewer or researcher selects a sample that reflects the characteristics of the whole population

Question 25

What is opportunity sampling?

Answer 25

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 26

Advantages of quota sampling

Answer 26

• 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 27

Disadvantages of Quota Sampling

Answer 27

• 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 28

Advantages of opportunity sampling

Answer 28

• Easy to carry out

- Inexpensive

Question 29

Disadvantages of opportunity sampling

Answer 29

• Unlikely to provide a representative sample

- Highly dependent on the individual researcher

Question 30

List of places in Large Data Set

Answer 30

Camborne
Heathrow
Hurn
Leeming
Leuchars
Beijing
Jacksonville
Perth

Question 31

Units for daily maximum gust

Answer 31

Knots

Question 32

Units for daily maximum relative humidity

Answer 32

Given as percentage of air saturation

Question 33

Daily mean cloud cover units

Answer 33

Oktas

Question 34

Daily mean visibility units

Answer 34

Decametres - Dm

Question 35

Daily mean pressure units

Answer 35

Hectopascals - hPa