Four Commonly Misused Research Terminologies in Neurosurgery Research
Ignatius Esene, MD, PhD, MPH1,*; Ulrick S Kanmounye 2; Nqobile Thango, MD 3; Luxwell Jokonya, MD 4; Laurel Nague 5, Ahmed Negida, MD 6

1.Neurosurgery Division, Faculty of Health Sciences, University of Bamenda, Bambili, Cameroon.
2.Research Department, Association of Future African Neurosurgeons, Yaoundé, Cameroon.
3.Neurosurgery Division, Department of Surgery, University of Cape Town, South Africa
4.Department of Surgery, University of Zimbabwe, College of Health Sciences, Harare, Zimbabwe
5.Faculty of Medicine and Biomedical Sciences, Garoua, University of Ngaoundere, Cameroon
6.Zagazig University Hospitals, Zagazig University, El-Sharkia, Egypt.

Corresponding Author: Ignatius N Esene, MD, M.Sc, PhD, MPH, Neurosurgery Division, Faculty of Health Sciences, University of Bamenda, Bambili, Cameroon, P.O Box 812, Bamenda, Cameroon.

Copy Right: © 2022 Ignatius N Esene. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received Date: December 23, 2021
Published Date: January 01, 2022

Introduction

An accurate answer to a research question can only be obtained from a properly designed and reported study. A proper understanding and the use of research terminology is the fundamental foundation of any clinical study. We often get little exposure to research methods within the medical field, and it is often intimidating when faced with our first research project. Specific terminology such as retrospective/prospective is often misused by even well-seasoned epidemiologists (1 . Quite often in papers, authors use these terms synonymously with case-control and cohort studies, respectively, on the premise that the former looks backward from disease to a particular cause while the latter looks forward from exposure to an outcome (2). Other literature recommends using this temporal classification to refer simply to the relationship between the initiation of the study by the investigator and the occurrence of the disease or outcome (2). This holds true for case-control studies and helps to distinguish between retrospective and prospective cohort studies.
To eliminate this confusion and ensure consistency in the correct reporting of research, we have in this mini-review attempted to provide the updated definitions of four commonly ill-defined terminologies: prospective, retrospective, prolective, and retrolective. The use of correct research terminology is essential for the appropriate sorting and indexing of evidence, enhancing research quality and the proper application of scientific knowledge to patient care. The definition of the terminologies;-Exposure and Outcome are an essential pre-requisite for the understanding of the aforementioned four terminologies.

Defining the Exposure and the Outcome
Almost all clinical trials are non-aetiological studies because they assess the treatment outcomes. However, other risk assessment studies (cohort and case-control studies) can study disease etiology due to their observational nature. Therefore, cohort studies and case-control studies can be further categorized into etiological and non-etiological studies. The meaning of exposure and outcome differs between aetiological and non-aetiological studies (Table 1).

An exposure may represent an intervention to which individuals are subjected (e.g., surgery), a behavior (e.g., smoking), or an individual attribute (e.g., age, sex, and race) (3).

Exposure can be dichotomized as present or absent or may be presented as graded levels of exposure, such as blood pressures (e.g., the higher the blood pressure, the higher the risk for stroke).

The outcome refers to the disease state, event (.e.g. complication, recurrence), behavior, or condition associated with health under investigation(3). Common outcomes in neurosurgery are the extent of tumor resection, complications, or recurrences.

In cohort studies and trials, participants are selected based on exposure status, while in case series and case-control studies, they are sampled based on the disease or outcome status.

Prospective versus Retrospective
When a population group is studied, the terms retrospective and perspective can be applied for two different research tasks and are thus defined by two parameters: the study timing and directionality.

Timing
Timing refers to the temporal relationship between the initiation of the study by the investigator and the occurrence of the disease or outcome, as illustrated for cohort and case-control studies below (2).

Depending on whether the outcome of interest has occurred at the time the investigator initiates the study, cohort studies can be classified as prospective or retrospective. Cohort studies in which the exposure and outcome have already occurred at the time of study are termed retrospective, non-concurrent, or historical cohort studies, while those in which the outcome has yet to occur are called prospective or concurrent cohort studies (3). (Figure 1).

For case-control studies, the outcome and exposure have already occurred at the time of the study. Thus, they are described as retrospective studies. Most cases included in a case-control study are prevalent cases (i.e., include both new and old disease events). However, in the rare condition of the nested case-control study, investigators study the incident cases only (i.e., new disease events that occurred within a large prospective cohort study). These incident case-control studies are special because their temporality is prospective (2).

Directionality
Directionality is the investigation’s direction vis-à-vis exposure and outcome (Figure 1).
The cohort study design looks forward from exposure (intervention) to the outcome (disease) and is prospective. Cohort studies are equally known as longitudinal studies; this term emphasizes that patients are followed over time, or incidence studies, drawing attention to the basic measure of new disease events over time. Irrespective of the data collection method, a cohort study always includes a comparison between the exposed vs. the non-exposed group.

The case-control design looks backward from the outcome (disease) to the putative exposure (intervention). Thus, case-control studies are said to be retrospective (2). Irrespective of the data collection method, a case-control study always includes a comparison between the cases (the group with the outcome of interest) vs. the control group (the group without the outcome of interest).

Prolective versus Retrolective

Data collection for a study can be prolective or retrolective. Prolective describes the use of data collected in the future from the start of the study, and retrolective describes the use of data collected in the past from the start of the study. In prolective studies, data collection occurs after study planning and is sourced directly from the origin (e.g., questioning study subjects). On the contrary, retrolective studies use data from secondary sources, i.e., existing before the research is conducted, and usually use data recorded for purposes other than the study. These secondary sources include databases, admission and operative records, patient files (i.e., retrospective chart review). Of note, studies can combine both prolective and retrolective data collection. These study types are called ambilective studies, and as suggested, they use data from primary and secondary sources (4).

Cohort studies have an exposure-to-outcome directionality and are often prolective albeit can also be retrolective. Retrolective cohorts are also called historical cohort studies. Case-control studies, on the other hand, are generally retrolective but can also be prolective (4).

In conclusion, there is a clear distinction between the terms prospective versus retrospective and prolective versus retrolective.

References
1.Feinstein AR. Clinical biostatistics. XX. “The epidemiologic trohoc, the ablative risk ratio, and "retrospective" research”. Clin Pharmacol Ther. 1973;14(2):291-307.
2.Esene IN, Mbuagbaw L, Dechambenoit G, Reda W, Kalangu KK. “Misclassification of Case Control Studies in Neurosurgery and Proposed Solutions”. World Neurosurg. 2018.
3.Esene IN, Ngu J, El Zoghby M, Solaroglu I, Sikod AM, Kotb A, et al. “Case series and descriptive cohort studies in neurosurgery: the confusion and solution”. Childs Nerv Syst. 2014;30(8):1321-32.
4.Castilla-Peón MF, Ramírez-Sandoval JC, Reyes-Morales H, Reyes-López A. [Clinical research design and causality: does oral rotavirus vaccine cause intussusception?]. Bol Med Hosp Infant Mex. 2015;72(5):346-52.
5.Charles H. Hennekens, Buring JE. “Epidemiology in Medicine”. Philadelphia, PA Lippincott Williams & Wilkins.; 1987.