Data Collection

Question 1

Define population

Answer 1

The whole set of items that are of interest

Question 2

What is a census?

Answer 2

It observes or measures every member of a population

Question 3

Define sample

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

What are the advantages of a census? (1)

Answer 4

It should give a completely accurate result

Question 5

What are the disadvantages of a census? (3)

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 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 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

What is a sampling unit?

Answer 8

Individual units of a population

Question 9

What is a sampling frame?

Answer 9

A list of named/numbered sampling units of a population

Question 10

Describe what is meant by random sampling

Answer 10

Every member of the population has equal chance of being selected

∴ the sample should be REPRESENTATIVE

And also helps remove BIAS

Question 11

What are the three methods of random sampling?

Answer 11

Simple random sampling

Systematic sampling

Stratified sampling

Question 12

What 3 things do you need for a simple random sample?

Answer 12

A sampling frame

Where each person or thing is allocated a unique number

And a selection of these numbers is chosen at random

Question 13

What 3 things do you need for a simple random sample?

Answer 13

A sampling frame

Where each person or thing is allocated a unique number

And a selection of these numbers is chosen at random

Question 14

What are the 2 methods of choosing a selection of random numbers?

Answer 14

Generating random numbers

Lotterty sampling

Question 15

Describe systematic sampling

Answer 15

The required elements are chosen at regular intervals

From an ordered list

(eg. Population = 100, Sample size = 20, you would take every 5th person since 100/20=5)

The first person to be chosen should be chosen at random

(So the next would be 7, 12, 17 etc.)

Question 16

Describe stratified sampling

Answer 16

The population is divided into mutually exclusive strata (eg. males and females)

And a random sample is taken from each

The proportion of each strata sampled should be the same

The number sampler in a stratum=(number in stratum/number in population)×overall sample size

Question 17

What are the 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

What are the disadvantages of simple random sampling?

Answer 18

Not suitable when the population size or the sample size is large

A large sampling frame is needed

Question 19

What are the advantages of systematic sampling?

Answer 19

Simple and quick to use

Suitable for large samples and large populations

Question 20

What are the disadvantages of systematic sampling?

Answer 20

A sampling frame is needed

It can introduce bias if the sampling frame is not random

Question 21

What are the advantages of stratified sampling?

Answer 21

Sample accurately reflects the population structure

Guarantees proportional representation of groups within a population

Question 22

What are the 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

Question 23

What are the two types of non-random sampling?

Answer 23

Quota sampling

Opportunity sampling

Question 24

Define quota sampling

Answer 24

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