As a clinician, you have a tremendous source for writing ideas-the patients you see each day. -Robert B. Taylor, M.D.

Presentation of the rationale for a scientific or clinical study

The basis for any study lies in the hypothesis(es) or question(s) posed by the study. Evaluation of the proposal or the "Rationale" begins with the reasonableness of the hypothesis. That is, there must be clear logic supporting the hypothesis and any hypothesis must be clearly and unambiguously addressable and answerable by the methods proposed.
 
Any hypothesis should be supported by clear rationale. This rationale should be developed and based on previous sound and substantive experimental observation or data, logical argument, or consensus of opinion in the literature (roughly in decreasing order of plausibility). By properly developing the rationale the reader will have no question the hypothesis makes sense. In other words, all studies or experiments must be based on clearly posed questions. The Introduction of the paper is used to provide the rationale for these questions. One question should be posed as the primary research question or objective with secondary questions identified in their order of importance or relevance. 

The proposed rationale should detail how you expect your study will constitute a significant contribution. The rationale should provide a specific and compelling case for your work. Most new scientific studies or proposals for new clinical interventions are based on problems of incomplete knowledge or weaknesses of current clinical practice. Typical rationale for a clinical study would be to report entirely new data (uncommon), data designed to support or refute previously published (and explicitly noted) data, or data designed to address explicitly stated controversies in the literature. The rationale should clearly document these issues by citing prior literature. Use quantitative data such as rates of occurrence where appropriate. You needn't provide a tutorial on past works. Cite a representative but not exhaustive range of past literature. Attempts to do so typically leads to loss of focus and do not demonstrate a clear understanding of relevant knowledge. The reader wants to know what is known in the field that is relevant to your proposal. They do not want to know everything that is known in the field. After describing what is known in reader-friendly terms, it is then your job to point out what is not known and why it is important to know it.
 
In citing the literature you need not discuss either the methods or observations of those studies in any detail; rather, only note their conclusions (assuming you believe them valid). In developing scientific arguments it is important to focus on observations or conclusions throughout the manuscript, not authors. Eliminating authors' names as subjects or objects in sentences places the emphasis on the findings rather than the authors. To this end avoid or eliminate authors' names and study descriptions. After stating the conclusions cite the references with superscripting. Anticipate reviewer criticisms throughout. When you are aware of contradictory information, note that information and make an effective argument why it is not critical (e.g., flawed studies, not directly relevant, etc.). 

The development of the rationale naturally leads into the final paragraph of the Introduction. In the final paragraph of the Introduction you should explicitly and specifically state what questions you intend to address. When the reviewer has completed the Introduction, you want to have them feeling as if you had just told them a story: you understand the past, you understand the present, and because of your ideas, your study will improve our knowledge in the future.
 

Tips

• Begin all paragraphs with topic sentences.
• Emphasize a specific concept or point with each paragraph (and topic sentence).
• Insure logical flow of paragraphs (and topic sentences).
• Insure hypotheses are stated in the same words throughout the proposal.
• Tell a story.
• Consider writing the Introduction section as the last task in assembling the manuscript.

Avoid

• Justifying a study by vaguely stating, "...to increase our understanding" - be specific.
• Referring to statements as "hypotheses" when they will not be tested - you will confuse the reviewer as to precisely what you are testing and what you are not.
• Making repetitive statements (readers are busy and don't like to read the same thing many times).
• Excluding key observations or references.
• Inventing jargon: Use plain English and the simplest word possible which accurately conveys.
• Making non-substantive statements. These do not lend clarity. Such a statement might include: "Many investigators have studied..." - rather state upfront what they (as a group) concluded.