The Internet has given us access to an unprecedented amount of information, but this development also facilitates the spread of misinformation if we do not think critically and evaluate what we read. The third edition of this classic textbook has been revised based on developments in biomedical research practices over the past decade to provide readers with the most up-to-date resource for navigating the ever-expanding world of dental literature. The book covers rhetoric and logic, the scientific method, components of scientific papers, research strategies, probability and statistics, diagnostic tools and testing, and experiment design. The chapter about searching the dental literature has been updated with the most current resources and search techniques available. A new chapter about clinical decision making uses a decision tree analysis with worked-out calculations to show how critical thinking skills can be used to select the most appropriate treatment decision in a clinical scenario; this is followed by a whole chapter of exercises in critical thinking. This book emphasizes how readers can practically apply critical thinking skills to evaluate scientific literature and thereby make the most informed decisions for their patients and themselves.
Donald Maxwell Brunette, PhD (Medical Biophysics), is a professor in the Department of Oral Biological and Medical Sciences and a former associate dean of Research and Graduate Studies in the Faculty of Dentistry, University of British Columbia. A founding member of the Medical Research Council (Canada) Group in periodontal physiology directed by Prof A.H. Melcher at the University of Toronto, Prof Brunette has published more than 90 articles in refereed journals and has won awards from the International Association of Dental Research, Association of Canadian Faculties of Dentistry (W.W. Wood Award for Excellence in Dental Education), and the American Medical Writers Association (for the first edition of Critical Thinking). His research encompasses several fields, including citation analysis and clinical studies of breath odor, but mainly concerns cell-biomaterial interactions. He serves as a consultant to three biomaterials-related journals as well as the American Dental Association's Council on Scientific Affairs, and he has been a member, chair, or scientific officer of grant evaluation committees of the Canadian Institutes of Health Research as well as the National Science Foundation (USA).
Scientific Method and the Behavior of Scientists
Thou hast made him a little less than angels."
Because there is no one scientific method, any account of scientific method is bound to be incomplete or even inaccurate and misleading. Sir Peter Medawar, a Nobel laureate, has stated that "there is no such thing as a calculus of discovery or a schedule of rules which by following we are conducted to a truth."1 Discoveries are made by individual scientists, who often have their own original and distinctive ways of thinking, and they do not necessarily follow any rigid protocol of scientific method.
The simple view advanced by Bronowski2 is that scientific method is organized common sense, and indeed this concept is emphasized in this book. However, the inclusion of the term organized is not a small addition, for scientific method differs from common sense in the rigor with which matters are investigated. For example, precise operational definitions, procedures to quantify, and theories to explain relationships are often employed, and a great effort is made to avoid inconsistencies. Results should be subject to the systematic scrutiny of the investigator or other scientists, and limits on how far the results can be applied should be sought. Formal methods for describing scientific method are still the topic of philosophic examination. But philosophic speculation or practice do not greatly concern typical research scientists, who are largely occupied in puzzle solving3 and who often seem too busy to consider how they got from A to B or how their investigational strategies relate to any philosophic concepts. There is increasing recognition that a key aspect in the development and acceptance of scientific facts and theories is the social interaction among scientists. Descriptions of an ideal exist for both the scientific method and the behavior of scientists, but the ideal does not always correspond with reality. Nevertheless, as they are the norms they will be discussed here.
The Behavior of Scientists
The everyday life of a scientist
In his chapter on discovery, Fred Grinnell gives a good account of how a working scientist operates.4 In brief, Grinnell started out on a project to study citric acid cycle enzymes under conditions of altered energy metabolism in rat liver cells. Such studies typically involve inhibitors, and Grinnell found that the addition of one inhibitor, arsenite, to the incubation medium had a surprising result, namely the cells to be cultured did not stick to the dish. This unexpected finding held a possible means to investigating a larger problem of interest, namely investigating the mechanisms of cell adhesion. After consulting with senior colleagues, Grinnell became convinced that cell adhesion was an important issue and proceeded to look at the problem in more detail. The chapter on discovery documents Grinnell's initial studies by including pages from his lab book and photomicrographs. Initially the reader might not be impressed by the quality of the micrographs or the messiness of the lab books that do not at all look like the polished pages of a published paper. But as the project proceeded, the quality of the photomicrographs was improved and enabled Grinnell to notice and quantify changes in cell shape, in particular that treatment of cell culture surfaces with serum enabled the cells not just to attach in the form of rounded cells but to spread out. So now Grinnell had a system in which cell adhesion could be altered by a known treatment and the various possible mediators of the spreading effect of serum dissected out and tested. Eventually Grinnell contributed to the discovery and elucidation of function of the biologic adhesion protein fibronectin, and helped to establish the importance of fibronectin in wound repair. In these early experiments though we can see some of the essential issues and processes of the working scientist. First, there was a concentration of interest on an important problem. Second, there were unexpected novel findings that the investigator realized had potential for further investigation, and third, there was a refinement of technique so that the biologic processes could be measured and dissected. Fourth, there were decisions that had to be made, such as discontinuing the original line of investigation when a more interesting aspect emerged. Fifth, there were no rules or grand plan that were slavishly followed but rather an interactive approach between what was found and what was best done next to solve a problem. Inherent in the description, as well as other parts of Grinnell's book, is that solving scientific puzzles is fun and that indeed, researchers feel their job could best be described as "how to get paid for having fun." Hold the attractive thought that on a day-to-day basis a researcher is having fun as we consider some of the other issues in scientists' behavior that are uncommon and sometimes less than pleasant.
Aspects of the sociology of science
The pioneer sociologist of science, Merton,5 identified six guiding principles of behavior for scientists:
1. Universalism refers to the internationality and independence of scientific findings. There are no privileged sources of scientific knowledge6; scientific results should be analyzed objectively and should be verifiable and repeatable. In practice, this norm means that all statements are backed up by data or citations to published work. Internationalism is one of the characteristics of modern science that emphasizes collaboration; papers frequently have multiple authors from different institutions and countries.
2. Organized skepticism describes the interactions whereby scientists evaluate findings before accepting them. Ideally, scientists would check results by repeating the observations or experiments, but this approach is time consuming and expensive. At the very least, scientists try to determine whether reported results are consistent with other publications. An ironclad rule of science is that when you publish something, you are responsible for it. When a finding is challenged, the investigator must take the criticism seriously and consider it carefully, regardless of whether the investigator is a senior professor and the challenger the lowliest technician or graduate student.7
3. Communalism is the norm that enjoins scientists to share the results of their research. "Scientific knowledge is public knowledge, freely available to all."6 One factor acting against the free exchange of information in a timely manner is the growing commercialization of scientific research. As both the institution and the principal investigator may benefit financially by obtaining rights to intellectual property, the time required to obtain patents results in delays in transmitting findings to the scientific community.
4. Disinterestedness is summed up by the dictum "Science for science's sake." At present, this norm appears to be honored more in breach than in observance. As noted previously, many scientists patent their discoveries and form alliances with commercial interests. At one time, I served on a grants committee that dispersed funds for major equipment. It happened that two applications from the same institution requested similar equipment, although there was not enough work to justify this duplication. One panel member wondered why the two groups did not combine and submit a single application. As it turned out, the two university-based principal investigators collaborated with different commercial interests and wanted a barrier between their laboratories. Ideally, scientists should not have any psychologic or financial stake in the acceptance or rejection of their theories and findings.
5. Humility is derived from the precept that the whole of the scientific edifice is incomparably greater than any of its individual parts. This norm is in operation whenever scientists receive awards; they inevitably thank their coworkers in glowing terms. Scientists giving invited lectures in symposia are generally at pains to point out which graduate students or postdoctoral researchers actually did the work and include lab pictures in their presentations to share the glory (small though it may be).
Despite the norm of humility, clashes of egos still occur. Several rules of behavior govern the interaction of scientists in the case of a disagreement. Discussion should be detached; that is, the issues, and not the personalities, should be discussed. The question is not who is right but rather what is right. The debate should be constructive; for example, if a referee decides that a paper should be rejected, the referee's comments should indicate how the paper could be improved. Finally, scientists who disagree should be courteous; they can disagree without being disagreeable.
6. Originality is highly prized in science and features prominently in determining who wins awards and grants. Yet, originality is difficult to define precisely, and, as Merton8 noted, there is a "gap between the enormous emphasis placed upon original discovery and the great difficulty a good many scientists experience in making one." The originality of a scientific work can reside in the novelty of the hypothesis being investigated, the methods used to investigate it, as well as in the results obtained. Perhaps the most common scientific strategy-the transfer method-involves applying methods and concepts...