Topic 2B: Data and Presenting Information: Sampling

Question 1

What is random sampling?

Answer 1

This is data collected from a sample rather than a population

Question 2

What is a simple random sample?

Answer 2

This is a sample collected in such a way that every member of the population has an equal chance of being included and should therefore be free from bias

Question 3

What is a sampling frame?

Answer 3

A numbered list of all items in a population

Question 4

What is a census?

Answer 4

This is where the whole population is examined

Question 5

What is a simple random sample?

Answer 5

This is a sample selected in such a way that every member of the population has an equal chance of being included

Question 6

What is a sampling frame?

Answer 6

A numbered list of all items in a population

Question 7

What are the drawbacks of random sampling?

Answer 7

The selected items are subject to the full range of variations inherent in a population, and the sample may be unrepresentative

Sample may be scattered over a larger geographical area

An adequate sampling frame may not exist

Question 8

What are three main methods of quasi-random sampling?

Answer 8

Systematic sampling
Stratified sampling
Multistage sampling

Question 9

What is systematic sampling

Answer 9

This is a sampling method which works by selecting every nth item after a random start, which is designed to give good approximation to random sampling

Question 10

What is the sampling interval?

Answer 10

The gap between every nth term

Question 11

What are the advantages of systematic sampling?

Answer 11

• Easy to select the sample items in a given sampling frame
• Reasonably random, providing no pattern to distribution of items

Question 12

What are the disadvantages of systematic sampling?

Answer 12

• Requires a sampling frame
• Requires access to the whole population
• If there is a pattern to the distribution of items, the sample may be biased
• May be expensive to select the random sample

Question 13

What is stratified sampling?

Answer 13

A sampling method which involves dividing the population into strata or categories. Random samples are taken from each stratum or category

Question 14

What are the advantages of stratified sampling?

Answer 14

Samples are representative as all important groups will have elements in the final sample

The sample structure represents the population as the same proportion of individuals should be chosen from each strata

Each stratum is represented by a randomly chosen sample

Increased precision

Question 15

What are the disadvantages of stratified sampling?

Answer 15

Time consuming to divide the population into strata

Prior knowledge required of each items in the population to determine strata

Question 16

What is multistage sampling?

Answer 16

A probability sampling method which involves dividing the population into a umber of subpopulations and then selecting a small sample of these subpopulations at random. each subpopulation is then dividing further and then a sample again is divined at random, with the process being repeated as many times as is required

Question 17

What are the advantages of multistage sampling?

Answer 17

Approximates to a random sample

Does not require a sampling frame

suits large populations

Cheap as samples may be collected quickly

Question 18

What are the disadvantages of multistage sampling?

Answer 18

Not truly random

The sample may be biased if only a small number of regions are selected.