Study design: what’s in a name? (2023)

Abstract

The name of the study should properly reflect the actual conduct and analysis of the study. This short paper provides guidance on how to properly name the study design. The first distinction is between a trial (intervention given to patients to study its effect) and an observational study. For observational studies, it should further be decided whether it is cross-sectional or whether follow-up time is taken into account (cohort or case–control study). The distinction prospective-retrospective has two disadvantages: prospective is often seen as marker of higher quality, which is not necessarily true; there is no unifying definition that makes a proper distinction between retrospective and prospective possible.

For new-borns, parents can choose, within certain limits, whatever name they consider appropriate and nice. This is, however, not the case when naming the design of a research project, as here the name should properly reflect the actual conduct and analysis of the study. And even though reporting guidelines like STROBE (1) provide guidance, design mislabelling still occurs. In the present paper, we propose four sequential questions (see also Fig. 1), the answers to which will guide the proper naming of the design.

Study design: what’s in a name? (1)

Study design: what’s in a name? (3)

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Flow-chart to determine the design of a clinical study.

Citation: European Journal of Endocrinology 183, 6; 10.1530/EJE-20-0873

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Is it a trial or an observational study?

The first question is whether the study assesses the effect of an intervention. If not, it is not a trial. If an intervention is studied, the next question is, whether the intervention was given to patients with the aim to study its effect or whether the study merely reflects the assessment of actual care. In the first case the study should be labelled as trial, in the second case the study is observational. For example, the effect of levothyroxine in subclinical hypothyroidism can be studied by randomizing patients to levothyroxine or placebo (trial), or using data from routine care (observational study). The difference can also be viewed from an ethical point of view: in a trial, patients should consent to be treated, in an observational study the patient should consent to have their data used for research purposes.

In a strict sense, a trial does not necessarily includes a control group, and also randomization is not a distinguishing feature of a trial; so called single arm trials lack both a control group and randomization. An example of a single arm trial would be a study of Cushing’s disease with a new and fancy drug, where cortisol levels are compared before and after 12 weeks treatment.

Although we generally tend to think of interventions as drugs, or surgical procedures, the range of potential interventions is much broader and also diagnostic strategies can be studied as interventions. For example, in MEN 1 syndrome, one could compare mortality and quality of life between family members who are tested for the gene mutation and family members who are not tested. In principle, such testing could also be studied in a randomized trial design.

Does the study take follow-up time into account?

The next question for classification of the study design is whether the study assesses the relation between exposure (e.g. potential risk factors) and outcome (e.g. development of disease) at one point in time, or whether that relation is studied longitudinally. For example, growth hormone (GH) levels can be related to glucose levels measured at the same time, or can be related to glucose levels (or diabetes status) after a specified follow-up period. Studies that assess a relation at one moment in time are called cross-sectional. If follow-up time is taken into account, the study is longitudinal (being either a cohort or a case–control study, see below). Clinical trials are always longitudinal.

It is relevant to distinguish the timing of the actual measurement of exposure and outcome, from the question how exposure relates to the outcome in terms of follow-up time. Consider the question whether smoking is a risk factor for adrenal incidentalomas. One could ask all incidentaloma patients, at time of diagnosis, about past smoking behaviour. Although measurements of exposure and outcome are made at the same time, the study takes follow-up time into account, as it aims to measure past smoking behaviour (before the development of the incidentaloma). A similar reasoning applies to variables that can reasonably be assumed stable over time (genes, sex); however, if GH levels (exposure) are related to glucose levels measured at the same time, the study is better labelled cross-sectional, since GH levels cannot be assumed to be stable over time.

it is important to note that it is the actual analysis that determines the answer to the question above. It can be the case that the relationship between GH and glucose levels are analysed based on baseline data from a randomized controlled trial. In this case, the original design of data collection may suggest that the study is longitudinal, yet since all baseline measurements are made at the same time, the study that answers this particular relation is in fact cross-sectional, despite the fact that the data come from a trial. Similarly, if laboratory data used for analysis are collected at one point in time from all Cushing patients in a hospital, this should be classified a cross-sectional study, even though researchers may be inclined to call their group of study patients a cohort. Diagnostic test accuracy studies can be seen as a specific type of cross-sectional studies.

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Are individuals sampled into the study based on exposure or based on outcome?

GH levels, or acromegaly, are often studied as potential risk factors for colon cancer. Researchers have two options when designing their study: they can compare patients with the exposure (high GH levels) to patients unexposed (normal GH levels) and assess whether the risk of developing colon cancer is higher in exposed patients. They can also start by sampling patients with the outcome (colon cancer) and compare their exposure levels (for example GH levels) to exposure levels of subjects without the outcome (i.e. without colon cancer). In the first situation, comparing outcome risk between groups of exposed and unexposed subjects, the design is called a cohort study. In the second situation, comparing levels of exposure between patients with and without the outcome, the design is a case–control study (see (2) for details).

Especially the term 'case–control study' is frequently used incorrectly. Often, so called case–control studies are in fact cohort studies; whereas also true case–control studies go without proper naming. The reason for this ‘case–control confusion’ (3) stems likely from the fact that clinicians think of cases as persons with a disease. In a cohort study assessing the potential increased risk for infections in Cushing’s disease, for example, compared to people without Cushing’s disease, the fact that patients with Cushing’s disease are considered ‘clinical cases’ does not classify the study as a case–control study. In fact, it classifies as a cohort study.

The defining feature of a cohort study is thus that individuals are followed over time and the risk for (developing) the outcome is estimated for a group of exposed subjects only, or is estimated for a group of exposed as well as a group of unexposed individuals. This means that a control group is not a necessary feature of a cohort study (4). Assessing the risk of acromegaly recurrence after surgery classifies as cohort study, even when no control group is included.

Prospective or retrospective does it matter?

Cohort studies are often labelled as either retrospective or prospective. However, this retrospective–prospective distinction has two disadvantages: prospective is often seen as marker of higher quality, which is not necessarily true; but more fundamentally, there is no unifying definition that makes a proper distinction between retrospective and prospective possible (1).

Often, the implicit definition of a retrospective design is that the study idea and conception of the study come after the data have been collected. The prototype of such retrospective study would for example be a cohort study assessing the association between GH levels and diabetes occurrence where researchers have to look in historic patient records to extract GH data. Along this line, also an analysis based on data from a randomized trial in which GH levels were measured and later related to diabetes occurrence, would need to be classified as retrospective if the idea for this additional analysis was not prespecified in the protocol. However, the data quality will likely differ between the two approaches: non-standardized GH measurements with missing data in the former vs standardized GH measurements and protocolized follow-up in the latter example. This shows that retrospective is not necessarily a marker for low quality data collection. In countries where almost all medical data is routinely collected in large databases (for e.g. in Denmark (5)) the distinction retrospective–prospective is also non-informative.

Better than to use the retrospective–prospective distinction, is to describe in detail how the study was designed, how the data were collected, and what potential weaknesses of the study are. Such a fully transparent approach is the best guarantee that the reader can judge the quality of the data and the conduct of the study.

Declaration of interest

O M D is a Deputy Editor for European Journal of Endocrinology. He was not involved in the review or editorial process for this paper, on which he is listed as an author.

Funding

This work was supported by grants from the Netherlands Organization for Scientific Research (ZonMW-Vidi project 917.16.430) and the LUMC.

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References

FAQs

What are the types of study design? ›

Broadly speaking, there are 2 types of study designs: descriptive studies and analytical studies.

What are the 4 major clinical research designs? ›

Clinical trials are further divided into randomized clinical trial, non-randomized clinical trial, cross-over clinical trial and factorial clinical trial.

What are the elements of study design? ›

... and colleagues described 4 key elements of study design, namely (1) patients, (2) interventions (exposure), (3) outcomes and (4) study methods [24]. The exposure studied in the review of observational studies differed from the exposure studied in the review of RCTs (Table 2).

What are the 4 types of study design? ›

There are four main types of Quantitative research: Descriptive, Correlational, Causal-Comparative/Quasi-Experimental, and Experimental Research. attempts to establish cause- effect relationships among the variables. These types of design are very similar to true experiments, but with some key differences.

What are the 5 examples of research design? ›

A Detailed Guide to Five Common Types of Research Design
  • Experimental design. ...
  • Correlational design. ...
  • Descriptive design. ...
  • Diagnostic design. ...
  • Explanatory design.
28 Jul 2022

What are the 10 types of research design? ›

Introduction
  • General Structure and Writing Style.
  • Action Research Design.
  • Case Study Design.
  • Causal Design.
  • Cohort Design.
  • Cross-Sectional Design.
  • Descriptive Design.
  • Experimental Design.
7 Sept 2022

What are the 9 types of experimental designs? ›

The main experimental designs are:
  • The completely randomised design. ...
  • The randomised block design. ...
  • Latin square designs. ...
  • Factorial designs. ...
  • Split plot designs. ...
  • Repeated measures designs in which each experimental unit is measured several times without different treatments being applied and time effects are of interest.

What are the 7 types of research? ›

Classification of Types of Research
  • Theoretical Research. ...
  • Applied Research. ...
  • Exploratory Research. ...
  • Descriptive Research. ...
  • Explanatory Research. ...
  • Qualitative Research. ...
  • Quantitative Research. ...
  • Experimental Research.
2 Oct 2020

What are the 3 common research designs? ›

Exploratory research design. Descriptive research design. Causal research design (experiments)

What are the 3 types of studies? ›

We can divide scientific studies on relationships into three main types: survey-type, observational and experimental.

What are the 8 elements of design? ›

All visual designs are composed of eight elements (Point, Line, Shape, Form, Tone, Texture, Color, and/or Text). These elements are combined and arranged to create a desired visual appearance.

What are the 13 elements of design? ›

The elements, or principles, of visual design include Contrast, Balance, Emphasis, Movement, White Space, Proportion, Hierarchy, Repetition, Rhythm, Pattern, Unity, and Variety.

What are the 5 parts of experimental design? ›

The components of experimental design are control, independent variable and dependent variable, constant variables, random assignment and manipulation.

What are the 5 types of non experimental research design? ›

Nonexperimental research falls into three broad categories: single-variable research, correlational and quasi-experimental research, and qualitative research.

What are the 2 types of research design? ›

What are the main types of research design?
  • Correlational and descriptive designs are used to investigate characteristics, averages, trends, and associations between variables.
  • Experimental and quasi-experimental designs are used to test causal relationships.

What are the 6 research designs? ›

Six common qualitative designs are described in this chapter: phenomenological, ethnographic, grounded theory, historical, case study, and action research. Excerpts from published nursing studies are presented for each of these six types of qualitative research.

What are the 5 kinds of research across fields? ›

Field Research
  • Direct Observation.
  • Participant Observation.
  • Qualitative Interviews.

What are the 7 steps of experimental research design? ›

The Seven Steps of the Research Process
  • Identification of a research problem.
  • Formulation of Hypothesis.
  • Review of Related Literature.
  • Preparation of Research Design.
  • Actual experimentation.
  • Results and Discussion.
  • Formulation of Conclusions and Recommendations.

What are the 7 steps of experimental design? ›

What are the steps of DOE?
  • Set objectives.
  • Select process variables.
  • Select an experimental design.
  • Execute the design.
  • Check that the data are consistent with the experimental assumptions.
  • Analyze and interpret the results.
  • Use/present the results (may lead to further runs or DOE's).

What are the 3 components of experimental research designs? ›

In general, designs that are true experiments contain three key features: independent and dependent variables, pretesting and posttesting, and experimental and control groups.

What are the 9 parts of research? ›

A complete research paper in APA style that is reporting on experimental research will typically contain a Title page, Abstract, Introduction, Methods, Results, Discussion, and References sections. Many will also contain Figures and Tables and some will have an Appendix or Appendices.

What are the 4 types of research design PDF? ›

  • Exploratory or Formulative Research.
  • Descriptive Research or Statistical Research.
  • Explanatory Research.
  • Experimental Research or Analytical Research.
7 Oct 2016

How are studies classified? ›

The research is broadly classified into two main classes: 1. Fundamental or basic research and 2. Applied research. Basic and applied researches are generally of two kinds: normal research and revolutionary research.

What is the best study design? ›

Randomized clinical trials or randomized control trials (RCT) are considered the gold standard of study design. In an RCT, the researcher randomly assigns the subjects to a control group and an experimental group. Randomization in RCT avoids confounding and minimizes selection bias.

What are the 12 principles of design? ›

There are twelve basic principles of design: contrast, balance, emphasis, proportion, hierarchy, repetition, rhythm, pattern, white space, movement, variety, and unity.

What are the 10 main principles of design? ›

There are 10 principles of design in total! They're also known as the elements of visual design, and are: movement, balance, contrast, proportion, repetition, rhythm, variety, emphasis, harmony, and unity.

What are the 5 main design principles? ›

Principles of design
  • Balance.
  • Alignment.
  • Proximity.
  • Repetition.
  • Contrast.
27 Feb 2019

What are the 5 main design factors? ›

To help you on your way, we've put together a list of 7 important factors to be aware of when designing a product.
  • AESTHETICS. ...
  • ERGONOMICS. ...
  • MATERIALS. ...
  • MANUFACTURE. ...
  • MODULARITY. ...
  • SUSTAINABILITY. ...
  • PROTECTION. ...
  • PACKAGING & ASSEMBLY.

What are the 6 parts of an experiment? ›

The Six Steps
  • Purpose/Question. Ask a question.
  • Research. Conduct background research. ...
  • Hypothesis. Propose a hypothesis. ...
  • Experiment. Design and perform an experiment to test your hypothesis. ...
  • Data/Analysis. Record observations and analyze the meaning of the data. ...
  • Conclusion.
18 Feb 2020

What are the 6 parts of the scientific method? ›

What are the 6 steps of the scientific methods in order?
  • Make an observation (theory construction)
  • Ask a question. ...
  • Form a hypothesis (make predictions)
  • Run an experiment to test the hypothesis (gather data)
  • Analyze the data and draw conclusions.
  • Share your results, so other researcher can make new hypotheses.
23 Feb 2022

What are the 3 types of research design? ›

Exploratory research design. Descriptive research design. Causal research design (experiments)

What is the most common study design? ›

Cross sectional

This is the commonest study design used in general practice and research, in general. These studies are relatively easy to do, inexpensive and can be carried out in a short time frame.

What are the 2 main types of research design? ›

What are the main types of research design?
  • Correlational and descriptive designs are used to investigate characteristics, averages, trends, and associations between variables.
  • Experimental and quasi-experimental designs are used to test causal relationships.

What are the 5 components of a research? ›

research components, introduction, literature review, method, results, discussion, conclusion.

What is the strongest study design? ›

A well-designed randomized controlled trial, where feasible, is generally the strongest study design for evaluating an intervention's effectiveness.

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