28/11/2022 - Last update 20/04/2023

Quantitative studies

[reading time: 7 minutes]

In a very schematic way, it can be said that quantitative research is based on the collection and statistical analysis of numerical data extrapolated from the reality and carried out on a sample size large enough to allow the generalizability of the results.

Several types of study have been developed, responding to different needs and contexts, and it is up to the researcher to find the most suitable method on the basis of the research question.

  • Observational studies, including the cohort and case-control studies, involve a data collection without the intervention of the researcher: they can be descriptive, that is they can describe the frequency and evolution of a pathology within a population or they can be analytical, that is they can seek the link between the health status and other variables, as the effect of one or more presumed determining factors of the development of a specific disease.
  • Experimental studies, on the other hand, involve an active contribution of the researcher, which exposes the population to an intervention in order to evaluate whether this can modify the condition or the disease studied. The most known type of study, also estimated as the most reliable, is the randomized controlled trial.

The pyramid of evidence

Different indicative schemes have been developed and modified over time in order to try to put into perspective the fact that not all studies have the same “value”, including the pyramid of evidence reported here as an example.

The pyramid is divided into ascending levels and on each step different types of study are listed. Indicatively, going upwards, each level corresponds to a higher level of rigor, quality and reliability of the evidence, the confidence about the accuracy of the results increases, the statistical errors and the risk of bias decrease to a minimum.

Background information and expert opinions, which are not always sustained by a proper basic research and can be biased by personal convictions.

Case-control studies, case series and reports of clinical cases.

These studies are found on the second step of the pyramid.

In the case-control studies two homogeneous groups are compared, one of which has been exposed to a certain factor (the cases) and the other has not (the controls). A retrospective evaluation is then carried out to find the association between the factor analyzed and the outcomes set by the researchers.

An example of case-control in the osteopathic literature is the retrospective study by King et al.1 who compared the clinical records of 160 women who had received OMT during pregnancy to the clinical records of 161 women who had not received it. They evaluated the parameters concerning the presence of meconium in the amniotic fluid, preterm delivery, use of forceps and cesarean delivery, obtaining some statistically significant differences in favor of OMT.

On the same level as the case-control there are the case series and case reports. These descriptive studies, although located in a low part of the pyramid, may prove valuable in identifying unusual or new factors. However, it is necessary to carry out additional studies before generalizing the results.

An example of case series is the study published in 2020 by Mills et al.,2 who analyzed retrospectively the clinical records of nine patients undergoing laparoscopic cholecystectomy, noticing an association with some somatic dysfunctions in the lower hind ribs and dorsal spine, between T5 and T11, in right rotation and flexion and left lateral flexion. According to the authors this information could be useful for an early diagnosis in surgical patients and to intervene with OMT in order to reduce pain, to improve function and quality of life.

In the report of a clinical case, Barni et al.3 describe a 40-days-old infant with esophageal atresia and tracheoesophageal fistula, who received 7 biweekly OMT treatments, concluding that OMT proved to be effective and safe in reducing dysphagia symptoms and risk of aspiration.

Cohort studies are on the third step. This is generally a prospective study. It can study a group of subjects (cohort) and compare it with another group (parallel cohort) to answer questions on etiology and risks, or it can focus on an inception cohort, affected by a certain pathology with the predetermined aim to measure the relevance of the results. Retrospective cohort studies are also designed, in this case the data related to the onset and display of a pathology are collected after the events have taken place.

In 2021, in the osteopathic field, Abbey et al.4 have carried out a study on a single cohort of 256 patients presented in a new “course”, called OsteoMAP, which combines psychological interventions, informed with mindfulness and with manual treatment. The patients would receive information about techniques on pain self management, body awareness, and coping strategies. Significant improvements have been obtained in all four outcomes. measured with questionnaires and subjective data reported by the patients. The authors recommend carrying out pragmatic randomized controlled studies to confirm the results.

Next up in the pyramid there are the randomized controlled trials (RCT), which are considered the so-called gold standard of clinical research, in consideration of the methodological rigor that distinguish them.

These studies close the lower part of the pyramid, reserved to the so-called primary studies, that are all those single articles that provide original data and describe experimentations in the clinical practice.

The upper part of the pyramid hosts the so-called secondary studies, also called filtered studies or studies of second level. This kind of studies are not performed on patients, but they are searches, so to speak, that put order in the literature by summarizing and interpreting the primary studies.

In the pyramid model here examined the three upper levels are occupied by secondary studies, which filter the information published in original articles. The “critically-appraised individual articles” and “critically-appraised topics”, both of which provide brief summaries of information from the medical-scientific literature, prepared for the purpose of solving a question and referring respectively to a single article or to several articles relating to a given subject.

At the top of the pyramid we find the systematic reviews. This type of research identifies, evaluates and summarizes the data of single experimentations, with the aim to collect their results and, where possible, to combine them together in a meta-analysis.

The systematic reviews with meta-analysis are some of the sources based on which the Guidelines of the clinical practice are processed and constantly updated.

Other kind of studies

The above diagram and models are by no means exhaustive.

It is to be stressed not only that there are many more of them, not even mentioned here, but also that the medical science is a system not at all static and evolves over time, as witnessed by the changes produced over the last years by the advent of the biopsychosocial model, the reflections on the clinical reasoning, the approach of the systems medicine, the precision medicine and more. The elaboration of new types of study often corresponds to these kinds of developments.

Merely as a way of example and without any pretension to ascribe to the following examples a greater importance compared to the numerous other medical trials, here are two types of study:

  • The proof-of-concept (POC) studies, also called proof of principle studies, are small exercises, in which a project draft is realized to trace its protocol and test its underlying idea or hypothesis in order to demonstrate its feasibility, also supported by several tools at a later time.

In the osteopathic field the study by Cordano et al.5 can be mentioned. They have investigated the effect of 5 sessions of OMTh on the chronic symptoms of multiple sclerosis in a population of 22 participants, measuring the outcomes with various questionnaires. Statistical significant improvements have been found with regard to fatigue and depression.

  • The N-of-1 trials, coming from the theory of precision medicine, which evaluates each individual on the basis of their reactions to a disease and to drugs, and aims at personalizing prevention, diagnosis and therapy.

This kind of study involves a single patient, subsequently exposed to multiple reversible therapies, generally with a crossover design. The N-of-1 trial deals with the question of the interindividual variability in the response to therapy and aims at improving the clinical intervention, to then generalize it to patients with similar characteristics to those of the case studied.

For further information on this kind of investigation please refer, for example, to the 2021 study6 investigating the possibility to apply the the N-of-1 method to the research in the field of manual therapies and to the systematic review of some N-of-1 studies in the field of rare genetic diseases of neurodevelopment7.

For further in-depth analysis please refer to the volume edited by Francesco Cerritelli and Diego Lanaro8, and to the articles on scientific studies on


  1. King HH, Tettambel MA, Lockwood MD, Johnson KH, Arsenault DA, Quist R. Osteopathic manipulative treatment in prenatal care: a retrospective case control design study. J Am Osteopath Assoc. 2003 Dec;103(12):577-82.
  2. Mills M, Sevensma K, Serrano J. Osteopathic Manipulative Treatment for a Recognizable Pattern of Somatic Dysfunction Following Laparoscopic Cholecystectomy. J Am Osteopath Assoc. 2020 Oct 1;120(10):685-690.
  3. Barni A, Zecchillo D, Uberti S, Ratti S. Osteopathic Manipulative Treatment in a Paediatric Patient with Oesophageal Atresia and Tracheo-Oesophageal Fistula. Case Rep Gastroenterol. 2019 Apr 9;13(1):178-184.
  4. Abbey, H., Nanke, L., & Brownhill, K. (2021). Developing a psychologically-informed pain management course for use in osteopathic practice: The OsteoMAP cohort study. International Journal of Osteopathic Medicine, 39, 32-40.
  5. Cordano C, Armezzani A, Veroni J, Pardini M, Sassos D, Infante MT, Tacchino A, Lapucci C, Cellerino M, Calabrò V, Ciullo L, Nourbakhsh B. Osteopathic Manipulative Therapy and Multiple Sclerosis: A Proof-of-Concept Study. J Am Osteopath Assoc. 2018 Aug 1;118(8):531-536.
  6. Tsiormpatzis S. Is the N-of-1 method applicable in bodywork research? Lessons learned using a trial as a methodological pilot. J Integr Med. 2021 May;19(3):203-210.
  7. Müller AR, Brands MMMG, van de Ven PM, Roes KCB, Cornel MC, van Karnebeek CDM, Wijburg FA, Daams JG, Boot E, van Eeghen AM. Systematic Review of N-of-1 Studies in Rare Genetic Neurodevelopmental Disorders: The Power of 1. Neurology. 2021 Mar 16;96(11):529.
  8. Cerritelli F, Lanaro D. Elementi di ricerca in osteopatia e terapie manuali. Napoli: Edises, 2018.



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