Chapter One: Statistics

Question 1

Who will a census ask?

Answer 1

Everyone

Question 2

Who will a sample ask?

Answer 2

A representative subset

Question 3

Benefits of a census

Answer 3

Completely accurate in result (unless lying / leading question e.g., “Isn’t the film great?”

Question 4

Downsides of a census

Answer 4

1. Time consuming / expensive
2. Can’t be used when testing process destroys item (e.g., if apples are ripe you’d have to destroy)
3. Hard to process large quantities

Question 5

Positives of taking a sample

Answer 5

1. Less time consuming / expensive
2. Less data
3. Less people

Question 6

Negatives of taking a sample

Answer 6

1. Not as accurate
2. Subset may not represent a population if sample is too small.

Question 7

How could an experiment be improved?

Answer 7

Ask more people.

Question 8

Individual units of a population are known as what?

Answer 8

Sampling units.

Question 9

What is the list of all items called?

Answer 9

Sampling frame (not always possible e.g., everyone in Birmingham)

Question 10

What are the 3 random sampling methods?

Answer 10

Simple random sampling
Systematic Sampling
Stratified Sampling

Question 11

What do all random sampling methods require?

Answer 11

A sampling frame

Question 12

Why do all random sampling methods require a sampling frame?

Answer 12

To have a list to pick sampling units from.

Question 13

How to conduct a Simple Random Method

Answer 13

Random Number Generator or pick from a hat

Question 14

Advantages of simple random method

Answer 14

No bias
Easy and Cheap
Each sample has a known and equal chance of being chosen.

Question 15

Disadvantages of simple random method

Answer 15

Not suitable with a large population / sample size
Sampling frame needed

Question 16

How to conduct systematic sample

Answer 16

People chosen at a random interval from ordered list.

Question 17

Benefits of systematic sampling

Answer 17

Simple and quick
Suitable for large samples and populations.

Question 18

Disadvantages of systematic sampling

Answer 18

Sampling frame needed
Can introduce bias if not random (may miss out smaller populations)

Question 19

How does stratified sampling work?

Answer 19

Divide population into groups and pick using simple random sampling (select withing stratum).

Question 20

In stratified sampling, how do you calculate how many you should test within a subset?

Answer 20

(total from group / total overall) x number you want to sample in experiment

Question 21

Advantages of stratified sampling

Answer 21

Sample accurately reflects population structure
Guarentees proportional representative of groups in a population.

Question 22

Disadvantages of stratified sampling

Answer 22

Sampling frame needed
Population must be clearly classified into distinct strata.
Selection in strata suffers same disadvantages as simple random sampling.