There are two types of abstract: descriptive and informative. In the vast majority of cases, it is likely that your course leader would expect you to use an informative abstract style for dissertations and theses. However, since this is not always the case, we have briefly explained the differences between the types abstract styles in this section.
The descriptive abstract is an outline of your research. It can almost be thought of as a table of contents, albeit set out in paragraphs explaining what the reader should expect in each chapter of the dissertation (i.e., Chapter One: Introduction, Chapter Two: Literature Review, Chapter Three: Research Strategy, etc.). The aim of the descriptive abstract is to allow the reader to decide whether to read the whole dissertation or just dip into those chapters of particular interest. Whilst there is some sense to this abstract style in lengthy reports where some sections of such reports may not be relevant or of interest to the reader, it is a problematic style for undergraduate and master's level theses for a number of reasons:
The person marking your dissertation will read every chapter, so there is little point in outlining each chapter in the abstract.
Such a descriptive overview of each chapter usually takes place at the end of the first major chapter in your dissertation (i.e., Chapter One: Introduction). This is a more appropriate place to tell the reader what to expect in the coming chapters.
Since the descriptive abstract does not capture the true essence of your research (i.e., its purpose, its significance, the choices of research strategy you made, and the main findings), it fails to draw the reader in and make them want to read more.
For these (and other) reasons, descriptive abstracts are typically not used for dissertation abstracts.
The informative abstract captures the essence of your research. Whilst the person marking your dissertation will inevitably read your entire document, the informative abstract should, in principle, make this unnecessary; that this, the informative abstract captures all the critical detail about a dissertation.
Having finished reading an informative dissertation abstract, the reader should know everything from the purpose and motivations of your research, how the study was significant, the choices of research strategy that you made, and the main findings and conclusions that were drawn from it. Each of these components is discussed in more detail in the section: How to structure your dissertation abstract.
It is for these (and other) reasons that informative abstracts are not only used in the vast majority of unpublished dissertations and theses, but also those that are published in Master's Abstracts International. Whilst it is most likely that as an undergraduate or master's level dissertation student you will be expected to write an informative, not descriptive abstract, it would be wise to double-check your dissertation guidelines or ask your supervisor first.
In the section that follows, What the reader expects from your dissertation abstract, we explain what the person reading your abstract will expect from an informative abstract.