SECONDARY data is collected from external sources such as:
- TV, radio, internet
- magazines, newspapers
- reviews
- research articles
- stories told by people you know
There's a lot more secondary data than primary data, and secondary data is a whole lot cheaper and easier to acquire than primary data. The problem is that often the reliability, accuracy and integrity of the data is uncertain. Who collected it? Can they be trusted? Did they do any preprocessing of the data? Is it biased? How old is it? Where was it collected? Can the data be verified, or does it have to be taken on faith?
Often secondary data has been pre-processed to give totals or averages and the original details are lost so you can't verify it by replicating the methods used by the original data collectors.
In short, primary data is expensive and difficult to acquire, but it's trustworthy. Secondary data is cheap and easy to collect, but must be treated with caution.
