Stats; Data Collection

Question 1

Population

Answer 1

The whole set of items that are of interest.

Question 2

Census

Answer 2

Observes or measures every member of a population

Question 3

Sample

Answer 3

A selection of observations taken from a subset of the population, to find out about the population as a whole.

Question 4

Sampling frame

Answer 4

A list of individually named or numbered sampling units.

Question 5

Sampling units

Answer 5

Individual units of a population.

Question 6

Census; advantages

Answer 6

Should give a completely accurate result.

Question 7

Census; disadvantages

Answer 7

• Time consuming and expensive
• Cannot be used when testing process which destroys the item.
• Hard to process large quantity of data.

Question 8

Sample; advantages

Answer 8

• Less time consuming and expensive than census
• Fewer people required
• Less data to process

Question 9

Sample; disadvantages

Answer 9

• Data may not be as accurate

- Sample may be to small to give enough info about small sub-groups of the population.

Question 10

Random sampling methods

Answer 10

simple random sampling, systematic, stratified

Question 11

Random sampling

Answer 11

Every member of population has equal chance of being selected.
Representative of population.
Removes bias.

Question 12

Simple random sampling

Answer 12

This sample of size ‘n’ is one where every sample of size ‘n’ has equal chance of being selected.

Question 13

Simple random sampling; advantages

Answer 13

• Free of bias
• Easy and cheap to implement for small populations and samples.
• Each sampling unit has a known and equal chance of selection.

Question 14

Simple random sampling; disadvantages

Answer 14

• Not suitable for large population or samples sizes.

- Needs a sampling frame.

Question 15

Stratified sampling

Answer 15

The population is divided into mutually exclusive strata (e.g. males and females) and a random sample is taken from each.

Question 16

Stratified sampling; advantages

Answer 16

• Sample accurately reflects population structure.

- Guarantees proportional representation of groups within population.

Question 17

Stratified sampling; disadvantages

Answer 17

• Population must be clearly classified into distinct strata.
• Selection in each stratum has same disadvantages as simple random sampling.

Question 18

Systematic sampling

Answer 18

The required elements are chosen at regular intervals from an ordered list.

Question 19

Systematic sampling; advantages

Answer 19

• Simple and quick

- Suitable for large samples and populations.

Question 20

Systematic sampling; disadvantages

Answer 20

• Needs sampling frame

- Can introduce bias if the sampling frame is not random.

Question 21

Non-random sampling methods

Answer 21

quota sampling, opportunity sampling

Question 22

Quota sampling

Answer 22

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

Question 23

Quota sampling; advantages

Answer 23

• Allows a small sample to still be representative of the population.
• No sampling frame required.
• Quick, easy and inexpensive.
• Allows for easy comparison between different groups within a population.

Question 24

Quota sampling; disadvantages

Answer 24

• Non-random sampling can introduce bias.
• Population must be divided into groups, costly or inaccurate.
• Increasing scope of study increases number of groups, adds time and expense.
• Non-responses are not recorded as such.

Question 25

Opportunity (convenience) sampling

Answer 25

Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Question 26

Opportunity sampling; advantages

Answer 26

• Easy to carry out

- Inexpensive

Question 27

Opportunity sampling; disadvantages

Answer 27

• Unlikely to provide a representative sample.

- Highly dependent on individual researcher.