What are the different sources of "secondary data"?
(i) Published printed sources: There are a variety of published printed sources. Their credibility depends on many factors. For example, on the writer, publishing company, and time and date when published. New sources are preferred and old sources should be avoided as new technology and research bring new facts into the light.
Books: Books are available today on every subject. The use of books starts even before you have selected the topic. After the selection of topics, books provide insights on how much work has already been done on the same topic, and you can prepare your literature review. Books are a secondary source but the most authentic one in secondary sources.
Journals/periodicals: Journals and periodicals are becoming more important as far as data collection is concerned. The reason is that journals provide up-to-date information which at times books cannot and secondly, journals can give information on the very specific topic on which you are researching rather than broader topics.
Magazines/Newspapers: Magazines are also effective but not very reliable. Newspaper, on the other hand, is more reliable and in some cases, the information can only be obtained from newspapers as in the case of some political studies.
(ii) Published Electronic Sources: As the internet is becoming more advanced, fast and reachable to the masses, it has been seen that much information that is not available in printed form is available on the internet. In the past, the credibility of internet was questionable but today it is not the case. The reason is that in the past journals and books were seldom published on internet, but today almost every journal and book is available online. Some are free and for others you have to pay the price.
E-journals: e-journals are more commonly available than printed journals. Latest journals are difficult to retrieve without a subscription.
General Websites: Generally, websites do not contain very reliable information so their content should be checked for the reliability before quoting from them.
Weblogs are also becoming common. They are actually diaries written by different people. These diaries are as reliable to use as personal written diaries.
(iii) Unpubished Personal Records: Some unpublished data may also be useful in some cases.
(iv) Diaries: Diaries are personal records and are rarely available, but if you are conducting a descriptive research then they might be very useful. Anne Frank's diary is the best example of this, for the record of Nazi wars.
(v) Letters: Lettesrs like diaries are also a rich source but should be checked for their reliability before using them.