Sampling

Question 1

Simple random sampling

Answer 1

Sample of size n and every sampling unit has an equal chance of being selected
Using a sampling frame to randomly select sampling units

Pros: free of bias, easy and cheap for small populations/samples, each sampling unit has a known and equal chance of selection
Cons: when sample/population is large, is time consuming, expensive , sampling frame is required

Question 2

Systematic sampling

Answer 2

Required elements are chosen at regular intervals from an ordered list
Pros: simple and quick to use, suitable for large samples/populations
Cons: sampling frame required, can have bias if sampling frame isn’t random

Question 3

Stratified sampling

Answer 3

Population divided into mutually exclusive strata with equal proportions being sampled, random sample units taken from each

Pros: sample accurately reflects population structure, guarantees proportional representation of groups
Cons: population needs to be clearly classified into distinct strata, selection within the stratum has same disadvantages as random sampling

Question 4

Number sampled in a stratum =

Answer 4

(Number in stratum/Number in population) x overall sample size

Question 5

Quota sampling

Answer 5

A sample is selected that reflects characteristics across the whole population
Pros: small sample can still be representative of the whole population,
No sampling frame needed, quick, easy and inexpensive, allows for easy comparison between groups within a population
Cons: can introduce bias, requires division into groups which can be costly or inaccurate, can be time consuming and expensive from increasing scope of study, non-responses not recorded

Question 6

Opportunity sampling

Answer 6

Taking samples from those available at the time of study being carried out and fit criteria that is being looked for

Pros: easy to carry out, inexpensive
Cons: not likely to provide a representative sample, highly dependent on individual researcher

Question 7

Define a population

Answer 7

The whole set of items that are of interest

Question 8

Define a census

Answer 8

Observes or measures every member of a population

Question 9

Define a sample

Answer 9

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 10

Evaluate the use of a census

Answer 10

Pros: It should give a completely accurate result

Cons: Time-consuming and expensive, Cannot be used when the testing process destroys the item, hard to process large quantity of data

Question 11

Evaluate the use of a sample

Answer 11

Pros: Less time consuming and expensive than a census, fewer people have to respond, less data to process than a census

Cons: Data may not be as accurate, sample may not be large enough to give information about small sub-groups of the population.

Question 11

Define sampling units

Answer 11

Individual units of a population

Question 12

Define a sampling frame

Answer 12

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

Question 12

3 methods of random sampling are:

Answer 12

-Simple random sampling
-Systematic sampling
-Stratified sampling

Question 13

In simple random sampling what are two ways in which numbers are chosen?

Answer 13

Generating random numbers using a calculator, computer or random number table AND Lottery sampling

Question 14

2 types/methods of non-random sampling are:

Answer 14

-Quota sampling
-Opportunity sampling

Question 15

Variables or data associated with Numerical observations are called:

Answer 15

-Quantitative Variables or Quantitative Data

Question 16

Variables or data associated with non-numerical observations are called:

Answer 16

-Qualitative Data

Question 17

A variable that can take any value in a given range is a:

Answer 17

continuous variable

Question 18

A variable that can only take specific variables is a:

Answer 18

discrete variable