Information has three levels, primary, secondary and tertiary. Primary information is the original research information that comes straight from the researcher. It can be found in journal articles, conference proceedings, and research reports. It is the most authoritative, since it comes directly from the person doing the research, and the most timely, since it is the initial way in which research results are presented. The lag time between the research being completed and the information being published is usually less than 2 years.
Secondary information is compiled information.
It has been gathered from various sources and summarized into books and monographic series. It is less authoritative, since the books' authors and editors are not always the researchers who did the actual research, and it is less timely, since the information is usually gathered after the primary information has already been published in journals and conference proceedings. Tertiary information is synopsized information. It has been edited and condensed to provide basic information in the form of entries in dictionaries, handbooks and encyclopedias. It is not timely, and is the least authoritative since it is far removed from the original primary information.