Data Collection

Question 1

What is a population?

Answer 1

The set of items that are of interest e.g. the people in a town

Question 2

What is a census?

Answer 2

A census observes/measures every member of the population

Question 3

What is a sample?

Answer 3

• a selection of observations taken from a subset of the population used to find information about the population as a whole.

Question 4

What are the advantages of using a census?

Answer 4

• gives a completely accurate result

Question 5

What are the disadvantages of using a census? (3 points)

Answer 5

• time consuming + expensive
• cannot be used when the testing process destroys the item
• hard to process large quantity of data

Question 6

What are the advantages of using a sample? (3)

Answer 6

• less time consuming and expensive than a census
• fewer people have to respond
• less data to process than in a census

Question 7

What are the disadvantages of using a sample? (2)

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

How does the size of the sample affect the validity of conclusions drawn?

Answer 8

Larger sample = more accurate but need more resources

Question 9

What are sampling units?

Answer 9

• individual units of the population

Question 10

What is a sampling frame?

Answer 10

• a sampling frame are the sampling units named or numbered to form a list

Question 11

For random sampling what does every member of the population have an equal chance of ….

Answer 11

• equal chance of being selected

Question 12

What does random sampling help to remove?

Answer 12

• bias from a sample as each member of population has an equal chance of being picked

Question 13

What are the 3 methods of random sampling?

Answer 13

• simple random sampling
• stratified sampling
• systematic sampling

Question 14

What is a simple random sample?

Answer 14

• one where every sampling unit has an equal chance of being picked
• uses a sampling frame, allocate a number to each sampling unit.
• selecting a set amount of the numbers randomly (usually done using a calculator to randomly generate or using lottery sampling where the numbers are placed in a hat)

Question 15

What is systematic sampling?

Answer 15

• required elements are chosen at regular intervals from an ordered list.
• e.g. if a sample of size 20 is required from a population of 100 choose every 5th member because 100/20 = 5
• but first person is chosen at random

Question 16

What is stratified sampling?

Answer 16

• population is divided into mutually exclusive strata/ categories e.g. male and female
• a random sample is then taken from each in proportion to the total population

Question 17

What is the formula used to find the number of people/items in each strata for stratified sampling?

Answer 17

No of sampled in a stratum = number in stratum
——————————- X overall sample size
Number in population