Data collection

Question 1

Population definition

Answer 1

The whole set of items that are of interest

Question 2

What is a census?
(A&D)

Answer 2

Measures every member of the population

Advantage:
-Accurate result

Disadvantage:
-Expensive, time consuming
-Cannot be used when testing involves destroying items
-Hard to process large quantity of data

Question 3

Sampling units

Answer 3

Individuals of a population

Question 4

Sampling frame

Answer 4

List of sampling units

Question 5

What is a sample?
(A&D)

Answer 5

A selection of observations taken from a subset of population

used to find out more info about the population as a whole

Advantage:
-Less time consuming and cheaper
-Fewer people have to respond
-Less data needs to be processed

Disadvantage:
-Data may not be as accurate
-Sample may not be large enough to represent smaller subgroups of population

Question 6

Simple random sampling

Random sampling

What it is, advantages and disadvantages

Answer 6

-Each unit has an equal chance of being selected
-Using a random number generator/lottery sampling to generate sample and select items corresponding to the number produced

Advantage:
-Bias free
-Easy and cheap
-Each sample unit has a known and equal chance of selection

Disadvantage:
-Needs a sampling frame
-Not suitable for large samples and populations

Question 7

Systematic sampling

Random sampling

What it is, advantages and disadvantages

Answer 7

-Take every kth unit, k= size of population/sample size
-Generate a random number between 1 and k for starting point

Advantage:
-Quick to use
-Can be used for large samples and populations

Disadvantage:
-Needs a sampling frame
-Bias introduced if sampling frame is not random

Question 8

Stratified sampling

Random sampling

What it is, advantages and disadvantages

Answer 8

population is divided into mutually exclusive strata, and random samples are taken from each

-Sample represents the groups (strata) of the population
-(Sample size/ population size)*strata size for each strata
-Pick randomly

number sampled in a stratum= no. in strata/ no. in population * overall sample size

Advantage:
-Reflects population more accurately
-Proportional representation of group within population

Disadvantage:
-Population must be classified in strata

Question 9

Quota sampling

Non random sampling

What it is, advantages and disadvantages

Answer 9

Interviewer/researcher selects a sample that reflects the characteristics of the whole population

Advantage:
-No sampling frame
-Easy and inexpensive

Disadvantage:
-Not random, potential bias
-Non-responses not recorded

Question 10

Opportunity sampling

Non random sampling

What it is, advantages and disadvantages

Answer 10

-Quota is filled by those available at the time

Advantage:
-Easy and cheap

Disadvantage:
-Unlikely to be representative

Question 11

Qualitative data definition

Answer 11

Non numerical

e.g colour, type, shape

Question 12

Quantitative data definition

Discrete & continuous

Answer 12

Numerical

• Discrete - can only take specific values, e.g. shoe size
• Continuous - can take any decimal value

Question 13

Why is stratified sampling used?

Answer 13

To obtain a proportionally representative sample