Secondary data is the data that have been already collected by and readily available from other sources. Such data are cheaper and more quickly obtainable than the primary data and also may be available when primary data can not be obtained at all.

Advantages of Secondary data

1. It is economical. It saves efforts and expenses.
2. It is time saving.
3. It helps to make primary data collection more specific since with the help of secondary data, we are able to make out what are the gaps and deficiencies and what additional information needs to be collected.
4. It helps to improve the understanding of the problem.
5. It provides a basis for comparison for the data that is collected by the researcher.

Disadvantages of Secondary Data

1. Secondary data is something that seldom fits in the framework of the marketing research factors. Reasons for its non-fitting are:-
   1. Unit of secondary data collection-Suppose you want information on disposable income, but the data is available on gross income. The information may not be same as we require.
   2. Class Boundaries may be different when units are same.
      

      Before 5 Years	After 5 Years
      2500-5000	5000-6000
      5001-7500	6001-7000
      7500-10000	7001-10000

      Thus the data collected earlier is of no use to you.
2. Accuracy of secondary data is not known.
3. Data may be outdated.

Evaluation of Secondary Data

Because of the above mentioned disadvantages of secondary data, we will lead to evaluation of secondary data. Evaluation means the following four requirements must be satisfied:-

1. Availability- It has to be seen that the kind of data you want is available or not. If it is not available then you have to go for primary data.
2. Relevance- It should be meeting the requirements of the problem. For this we have two criterion:-
   1. Units of measurement should be the same.
   2. Concepts used must be same and currency of data should not be outdated.
3. Accuracy- In order to find how accurate the data is, the following points must be considered: -
   1. Specification and methodology used;
   2. Margin of error should be examined;
   3. The dependability of the source must be seen.
4. Sufficiency- Adequate data should be available.

Robert W Joselyn has classified the above discussion into eight steps. These eight steps are sub classified into three categories. He has given a detailed procedure for evaluating secondary data.

1. Applicability of research objective.
2. Cost of acquisition.
3. Accuracy of data.