Sampling definitions

Question 1

Census

Answer 1

A census observed or measures every member of a population

Question 2

Population

Answer 2

Population is the whole set of items that are of interest

Question 3

Sample

Answer 3

A sample is a selection of observations taken from a subset of the population which is used to find out the population as a whole

Question 4

Advantage of a census

Answer 4

It should give a completely accurate result

Question 5

Give 3 disadvantages of a census

Answer 5

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

Question 6

Give 3 advantages of a sample

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

Give 2 disadvantages of a sample

Answer 7

• the data may not be as accurate

- the sample may not be large enough to give information about small sub-groups if the population

Question 8

Sampling units

Answer 8

Individual units of a population

Question 9

Sampling frame

Answer 9

Sampling units of a population are individually named or numbered to form a list called a sampling frame

Question 10

Simple random sampling

Answer 10

A simple random sample of size n is one where every sample of size n has an equal chance of being selected. Every unit is allocated a unique number and these numbers are chosen at random by either generating random numbers or lottery sampling.

Question 11

Systematic sampling

Answer 11

In systematic sampling, the required elements are chosen at regular intervals from an ordered list. The first unit to be chosen should be chosen at random

Question 12

Stratified sampling

Answer 12

In stratified sampling, the population is divided into mutually exclusive strata (males and females for example) and a random sample is taken from each.
The size of each strata in the sample is proportional to the whole population in that strata

Question 13

Give 3 advantages of simple random

Answer 13

• 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 14

Give 2 disadvantages of simple random

Answer 14

• not suitable when the population size or the sample size is large as it it is potentially time consuming
• a sampling frame is needed

Question 15

Give 2 advantages of systematic sampling

Answer 15

• simple and quick to use

- suitable for large samples and large populations

Question 16

Give 2 disadvantages of systematic sampling

Answer 16

• a sampling frame is needed

- it can introduce bias if the sampling frame is not random

Question 17

Give 2 advantages of stratified sampling

Answer 17

• sample accurately reflects the population structure

- guarantees proportional representation of groups within a population

Question 18

Give 2 disadvantages of stratified sampling

Answer 18

• population must be clearly classified into distinct strata
• selection within each stratum suffers from the same disadvantages as simple random sampling

Question 19

Quota sampling

Answer 19

In quota sampling, an interviewer or researcher selects a sample that reflects the characteristics of the whole population. The population is divided into groups according to a given characteristic. The size of each group determines the proportion of the sample that should have that characteristic.

Question 20

Opportunity sampling

Answer 20

Opportunity sampling 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 21

Give 4 advantages of quota sampling

Answer 21

• allows a small sample to still be representative of the population
• no sampling frame is required
• quick and easy
• allows for easy comparison between different groups within a population

Question 22

Give 3 disadvantages of quota sampling

Answer 22

• non-random sampling can introduce bias
• population must be divided into groups, which can be costly or inaccurate
• increasing scope of study increase number of groups, which adds time and expense

Question 23

Give 2 advantages of opportunity sampling

Answer 23

• easy to carry out

- inexpensive

Question 24

Give 2 disadvantages of opportunity sampling

Answer 24

• unlikely to provide a representative sample

- highly dependent on individual researcher

Question 25

Continuous variable

Answer 25

A variable that can take any value in a given range

Question 26

Discrete variable

Answer 26

A variable that can take only specific values in a given range