Session 2 Sources of data
　　Main contents:
　　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..