Two types of abstracts exist in research. A "descriptive" abstract is usually 100 words or less and does not provide the reader with results or conclusions. This type of abstract usually precedes a humanities or social science paper that contains no measurable data. An "informative" abstract provides a complete picture of the body of work in 250 words for short documents, or in about 10 percent of the total word count for projects over 50 pages. This type of abstract most commonly precedes scientific research or social science papers that contain quantitative data, such as population data or survey information.
There are two reasons research papers contain an abstract. The first reason is searchability; an abstract contains keywords that allow search engines to identify relevant sources and topics. Titles do not often reflect the exact content of a body of work, and the probability that the words "politics" and "Russia" may occur anywhere in the full text of a random article are high. The second reason is to help the reader identify a useful source; by finding an accurate summary of the contents of a research paper, the reader can then decide if the entire work is worth reading or purchasing.
The abstract should contain all the information necessary for a reader to grasp the main idea of the paper without reading the entire work. The abstract tells the reader the purpose of the research, the hypothesis, how the research was conducted, the results of the research and any conclusions the author drew from the result. An abstract can also indicate any sources relevant to the research, such as "By comparing original copies of Grey's Anatomy to today's MRI technology, we conclusively proved that...." However, do not use an abstract as a bibliography.
A writer uses the introduction of her research paper to provide the reader with extensive background information on the subject of the research and create a thesis statement regarding the direction of the document and any questions to be answered; the introduction piques a reader's curiosity. An abstract, however, is full disclosure; an abstract should not leave the reader wondering how it all turned out or what the exact contents are.
Write the abstract after you finish the final draft of the research paper. Start by rereading the paper and highlighting points that you feel are important to the research, then set the paper aside and write a summary paragraph from memory. Do not concern yourself with exact mathematical figures. Compare the first draft to the highlighted points in the research paper and add in anything important you left out. Tighten up the language to fit within the word count and verify that you have included all keywords relevant to your research paper.