S2 Ch6

Question 1

3 types of population?

Answer 1

Finite - eg. No. of students at a school (can be numbered and counted)

Infinite - eg. No. of grains of sand on a beach (impossible to count)

Countably infinite - eg. No. of throws of a dice to obtain a 6 because theoretically the population could be infinite but we can count the individual members in it

Question 2

What is a census?

Answer 2

When information is obtained from all members of the population.

Question 3

Advantages of a census? (3)

Answer 3

• every single member of a population is used
• it is unbiased
• it gives an accurate answer

Question 4

Disadvantages of a census? (3)

Answer 4

• takes a long time to do
• it’s costly
• often difficult to ensure that the whole population is surveyed

Question 5

What is a sample?

Answer 5

A sub-set of a population that information is obtained from to represent a population.

Question 6

What is a sample survey?

Answer 6

An investigation using a sample.

Question 7

What are sampling units?

Answer 7

The individual units of a population.

Question 8

What is a sampling frame?

Answer 8

When the sampling units of a population are individually named or numbered.

Question 9

What are the advantages of sampling?

Answer 9

• if population is large and well mixed a sample will be representative of the whole population
• sampling is cheaper than taking a census
• sampling is advantageous where the testing of items results in their destruction (testing lightbulb lifetime)
• data is faster to retrieve with sampling

Question 10

Disadvantages of sampling? (2)

Answer 10

• uncertainty about sampling due to natural variation between any two samples (result of natural variation between individual units)
• bias can occur (only responses from people with certain interests, or if the person takes the sample chooses their family to take it rather than a fair sample)

Question 11

Define a statistic?

Answer 11

A statistic is a quantity calculated solely from the observations in a sample (doesn’t involve any unknown parameters).

Question 12

When is an equation not a statistic?

Answer 12

When it contains μ or σ etc.

Question 13

What is a sampling distribution?

Answer 13

The sampling distribution of a statistic gives all the values of a statistic and the probability that each would happen by chance alone.

Question 14

What is a population?

Answer 14

A collection of individual people or items.