Session 2 Sources of data Main contents: 1. Types of data 2. Secondary data 3. Sampling methods 2.1
1. Types of data
2. Secondary data
3. Sampling methods
2.1 Types of data
Data can be classified as follows:
(a)Primary and secondary data
Primary data – are data collected especially for a specific purpose.
Secondary data – are data which have been collected elsewhere, for some
other purposes, but which can be used or adapted for the
survey being conducted.
(b)Discrete and continuous data
Discrete data – are data which can only be taken on a finite or countable
number of values within a given range.
Continuous data – are data which can take on any value.
(c )Sample and population data
Sample data – are data arising as a result of investigating a sample
Population data – are data arising as a result of investigating the population.
2.2 Secondary data
The main sources of secondary data are: governments; banks; newspaper; trade journals; information bureau; consultancies; libraries and information services.
- It is essential to believe that the secondary data used is accurate and reliable.
2.3 Sampling methods
Data are often collected from a sample rather than from a population. If the whole population is examined, the survey is called a census.
There are two types of sampling methods:
Probability sampling method – is a sampling method in which there is a known chance of each member of the population appearing in the sample.
- Stratified random
If random sampling is used, it is necessary to construct a sampling frame.
A sampling frame should have following characteristics
- up to dateness
Non probability sampling method – is a sampling method in which the chance of each member of the population appearing in the sample is not know, i.e. quota sampling.
The following statements relate to which different types of data
(i). Secondary data are data collected especially for a specific purpose
(ii). Discrete data can take on any value.
(iii) Qualitative data are data that cannot be measured
(iv). Population data are data arising as a result of investigating a group of people or
Which of the statements are true?
Solution is D
It is primary data that is collected for a specific purpose so (i) is false. Continuous data can take on any value so (ii) is false. Both (iii) and (iv) are true.
Which of the following statements are not true?
I If a sample is selected using random sampling, it will be free from bias.
II A sampling frame is a numbered list of all items in a sample.
III In cluster sampling there is very little potential for bias.
IV In quota sampling, investigators are told to interview all the people they meet
Up to a certain quota.
A I, II, III and IV
B I, II and III
C II and III
D II only
Solution is C
A sampling frame is a numbered list of all items in a population (not a sample)
Cluster sampling involves selecting one definable subsection of the population which therefore makes the potential for bias considerable.