When planning any substantive piece of medical research, especially where human patients are involved, great care in the design of the research is required. Whilst the PPDAC methodological framework described above has broad applicability to such problems, there are specific considerations that make such exercises in the medical arena particularly problematic (e.g. see the discussion in Ercan et al., 2007 [ERC1]). Many of these are addressed through adoption, where practicable, of a procedure known as randomized controlled trials, or RCTs. In its simplest, and most widely used form, the RCT is a relatively straightforward procedure — at least, in theory! Other widely used forms of medical research include case-control studies and cohort studies. All three of these procedures are described in greater detail in the subsections that follow.
Assuming a trial or other form of study has been designed and is undertaken, the question of reporting all steps in the process is paramount. In recent years there has been a great deal of effort put into standardizing the registration of the details of trials (essentially metadata), and into structured reporting. This has been led by the academic community in association with all the major medical journals, and has led to a series of "statements" that are designed to both assist and direct the conduct of trials. Journals such as Annals of Internal Medicine, BMC Medicine, BMJ, Journal of Clinical Epidemiology, the Lancet, Obstetrics & Gynecology, Open Medicine, PLoS Medicine and Trials have all adopted and published guidelines for reporting randomized trials under the CONSORT or "Consolidated Standards of Reporting Trials" initiative. CONSORT 2010 is the latest version of these guidelines, and comprises specifically the process of reporting what was done and what was found (i.e. it does not include recommendations for designing, conducting or analyzing trials). Essentially CONSORT consists of a checklist for publication which covers: Title and abstract; Introduction; Methods; Randomization; Results; Discussion and Other information. It also includes a flow diagram "of the progress through the phases of a parallel randomized trial of two groups", which we have included below. More details can be found on the CONSORT website and in the references below. There are also a number of extensions to the CONSORT statement that provide guidance for different forms of trials, such as cluster trials (e.g. where treatments are applied to clusters, such as members of a family) and a number of other forms of trial.
CONSORT 2010 FLOW DIAGRAM
As noted above, RCT's are by no means the only, or always the best or most appropriate framework for the conduct of medical trials. In many instances the 'ideal' of a controlled experiment is not achievable, and many other forms of research are also widely used — for example cohort studies and case-control studies. However, the great advantage of RCT's is that they have been shown, within the strict confines of the trial in question, to be the best means for avoiding bias and minimizing confounding effects, enabling conclusions regarding the differences between outcomes to be made with a relatively high degree of confidence.
References and further reading
[ALT1] Altman D G, Bland J M (1991) Improving Doctors' Understanding of Statistics. J of the Royal Stat. Soc., A, 154(2), 223-267
[BH1] Bradford Hill A (1937) Principles of Medical Statistics. The Lancet, London (issued in various editions until 1971. Then republished as "A Short Textbook of Medical Statistics" in 1977
[BH2] Bradford Hill A (1965) The Environment and Disease: Association or Causation? Proc. of the Royal Soc. of Medicine, 58, 295-300. A copy of this article is reproduced on Tufte's website: https://www.edwardtufte.com/tufte/hill
[CAM1] Campbell M J, Machin D, Walters S J (2007) Medical Statistics : A Textbook for the Health Sciences. 4th Ed., John Wiley & Sons Ltd, Chichester
[ERC1] Ercan I, Berna Y, Yang Y, Ozkaya G, Cangur S, Ediz B , Kan I (2007) Misuage of Statistics in Medical research. Eur. J of Gen. Med., 4(3), 128-134
[EVA1] Evans A S (1976) Causation and Disease: The Henle-Koch Postulates Revisited. Yale J Biol Med., 49(2), 175-195
[GR1] Greenland S, Pearl J, Robins J M (1999) Causal Diagrams for Epidemiologic Research, Epidemiology,10(1), 37-48
[MRC1] Medical Research Council (1948) Streptomycin treatment of pulmonary tuberculosis. BMJ, 4582, 769-782
[PH1] Phillips C V, Goodman K J (2004) The missed lessons of Sir Austin Bradford Hill. Epidemiologic Perspectives & Innovations, 1(3)
[ROT1] Rothman K J, Greenland S, Lash T L eds. (2008) Modern Epidemiology. 3rd Ed., Lippincott Williams & Wilkins
[OLS1] Olson S H, Voigt L F, Begg C B, Weiss N S (2002) Reporting participation in case-control studies. Epidemiology,13(2),123-6
STROBE (Strengthening the Reporting of Observational studies in Epidemiology): https://www.strobe-statement.org/
CONSORT (Consolidated Standards of Reporting Trials) encompasses various initiatives to alleviate the problems arising from inadequate reporting of randomized controlled trials (RCTs): https://www.consort-statement.org
EQUATOR Network: https://www.equator-network.org/
Wikipedia: Randomized controlled trials: https://en.wikipedia.org/wiki/Randomized_controlled_trial