Version: 24.04.2020

Description of the document: This document is used as training material for the COVID-19 screening crowd. It will help the participants to identify study designs with brief study descriptions and some tips.

Epidemiological study designs:

Case Report

A case report is a detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient. Case reports usually describe an unusual or novel occurrence and as such, remain one of the cornerstones of medical progress and provide many new ideas in medicine.

Tips: If the study only mentions one patient in depth, consider choosing case report option.

Case Series

Observations are made on a series of individuals who share similar (exposure) characteristics. Case series can lack systematic enrollment and can select their participants ad hoc.

Tips: Be careful not to mix with cohort studies and case-control studies. The main difference is, in the case series there will be no control groups and sampling can be ad hoc.

Cohort Study

A study in which a defined group of people (the cohort) is followed over time. Participants are selected based on the exposure status to examine associations between different interventions received and subsequent outcomes.

Tips: Generally a prospective study design (not all the time). Participants are assigned into different groups based on their exposure. (e.g. Exposed, not exposed)

Case Control Study

A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest). In theory, the case-control study can be described simply. First, identify the cases (a group known to have the outcome) and the controls (a group known to be free of the outcome). Then, look back in time to learn which subjects in each group had the exposure(s), comparing the frequency of the exposure in the case group to the control group.

Tips: Generally a retrospective study design. The case-control study should have group of people which has the outcome and a comparison group which does not have the outcome. (e.g. comparing patients with COVID-19 which has been admitted to ICU (cases) and patients with COVID-19 which has not been admitted to ICU (controls))

Cross-sectional Study

In a cross-sectional study, the investigator measures the outcome and the exposures in the study participants at the same time, on one time-point per participant only. Unlike in case–control studies (participants selected based on the outcome status) or cohort studies (participants selected based on the exposure status), the participants in a cross-sectional study are just selected based on the inclusion and exclusion criteria set for the study. These studies generally lack follow-up time.

Tips: A scientific snapshot. All information regarding the participants collected at the same time. (e.g. A survey that assesses the psychologic stage of ICU nurses during the COVID-19 pandemic)

Diagnostic Study

A study where the primary aim is to evaluate diagnostic tests.

Ecological Study

In ecological studies the unit of observation is the population or community. Disease rates and exposures are measured in each of a series of populations and their relation is examined. Often the information about disease and exposure is abstracted from published statistics and therefore does not require expensive or time consuming data collection. The populations compared may be defined in various ways.( eg. Geographical comparisons, Time trends)

Tips: There should be no individual level data instead all data should be aggregated.


Studies that develop or present guidelines for different conditions. (e.g developing a testing guideline for Covid-19)

Modeling Study

An epidemiological model is usually defined as 'a mathematical and/or logical representation of the epidemiology of disease transmission and its associated processes'.

Mathematical modeling studies are frequently used to synthesize evidence from multiple data sources to address a clinical or public health question not directly addressed by a primary study. For example, a mathematical model was used to synthesize evidence obtained from virological, clinical, epidemiological, and behavioral data to help determine optimal target populations for influenza vaccination programs.

Outbreak or Surveillance report

Outbreak reports summarize how the outbreak was detected, the investigations that were conducted, the interventions that were carried out to control it, provide descriptive epidemiology and outcomes.

Surveillance reports provide essential information about a disease or health-related condition according to person, time and place. They often provide the basis to identify burden of illness and may include related information, such as trends in risk factor frequency or prescribing practices.

Qualitative Study

Qualitativemethods are used to answer questions about experience, meaning and perspective, most often from the standpoint of the participant. These data are usually not amenable to counting or measuring. Qualitative research techniques include 'small-group discussions' for investigating beliefs, attitudes and concepts of normative behaviour; 'semi-structured interviews', to seek views on a focused topic or, with key informants, for background information or an institutional perspective; 'in-depth interviews' to understand a condition, experience, or event from a personal perspective; and 'analysis of texts and documents', such as government reports, media articles, websites or diaries, to learn about distributed or private knowledge.

Tips: If you see an interview being conducted consider choosing qualitative study option.

Review (Systematic Reviews, Rapid Reviews, Narrative reviews) (field: Epidemiology)

A review is an overview of published research.

Narrative reviews lack systematic components and provide an overview of evidence in a narrative or 'story'.

Rapid and Systematic Reviews: Typically involve a detailed and comprehensive plan and search strategy derived a priori, with the goal of reducing bias by identifying, appraising, and synthesizing all relevant studies on a particular topic. Systematic reviews can include a meta-analysis which involves using statistical techniques to synthesize the data from several studies into a single quantitative estimate or summary effect size.

Tips: All review types including Narrative Reviews, Rapid Reviews, Systematic Reviews about epidemiologic aspect of the COVID-19 should be included this section.


In a clinical trial, participants receive specific interventions according to the research plan or protocol created by the investigators. These interventions may be medical products, such as drugs or devices; procedures; or changes to participants' behavior, such as diet. Clinical trials may compare a new medical approach to a standard one that is already available, to a placebo that contains no active ingredients, or to no intervention. Some clinical trials compare interventions that are already available to each other. When a new product or approach is being studied, it is not usually known whether it will be helpful, harmful, or no different than available alternatives (including no intervention). The investigators try to determine the safety and efficacy of the intervention by measuring certain outcomes in the participants. For example, investigators may give a drug or treatment to participants who have high blood pressure to see whether their blood pressure decreases.

Tips: The main difference in this study design is that interventions are giving by the investigators to participants.

For this section we are not looking for randomization and blinding requirements all trials including, Randomized controlled trials, Blind trials Non-blind trials, Adaptive clinical trials, Nonrandomized trials should be included in this section.

EPI: Other

Studies in the field of epidemiology where no other definition of study design matches. We discourage you to use this category

Basic research/non-epidemiological study designs:

Basic: Animal Experiment

Studies that use animal models to answer scientific questions (in vivo experiments).

Basic: In Vitro Experiment

In vitro comes from the Latin term "in glass." The term refers to studies of biological properties that are done in a test tube (i.e. in a glass vessel) rather than in a human or animal. In vitro studies allow scientists to isolate specific cells, bacteria, and viruses and study them without the distractions of having to look at a whole organism.

Basic: Biochemical/Protein Structure Studies

Biochemical analysis techniques refer to a set of methods, assays, and procedures that enable scientists to analyze the substances found in living organisms and the chemical reactions underlying life processes

Protein Structure studies' research topics include the study of proteins, which, as components of the cytoskeleton of a cell, give the cell its shape and enable its movements; the study of membrane proteins that determine which substances must be transported into or out of a cell and how signals are transferred into a cell. Apart from their own research on protein structures, researchers are also involved in the development of new techniques for determining protein structures

Basic: Sequencing and Phylogenetics

Phylogenetic analysis is the study of evolutionary relationships among molecules, phenotypes, and organisms. On a more practical level, phylogenetic analysis of protein sequence data is integral to gene annotation, prediction of gene function, the identification and construction of gene families, and gene discovery.

Basic: Within-Host Modelling

Depending on the pathogen being studied, the basic model of pathogen dynamics must include certain characteristics that are 'basic' to the disease dynamics in-host. These include, for example, the cells that the pathogen infects, the existence of the pathogen in the host (i.e. in what areas of the body pathogen particles may reside in), the time-scale of the infection of the host (i.e. long-lived and persistent (chronic) or short-lived (acute) infections) and the life-cycle of the pathogen (which includes all of the different methods by which the pathogen can produce progeny).

Basic: Research Review

Reviews in other fields than epidemiology

Basic: Other

Basic research or fundamental research that cannot be captures in of the other basic research categories.

Non-original research:

Comment, editorial, …, non-original

Commentaries, Editorials, view-points, opinions, or new items are publications that present a summary of other data, or opinions and generally lack original data. When original data is presented in such a form, please chose a study design that reflects the function and not the form (i.e. when someone reports a case in a letter, which the publisher decides to call a 'comment' this would still hold the information of a case-report).

Example of a 'comment' that reports original data, and thus should be qualified as a cross-sectional study: