The research pyramid and how to select the best type of study

In the science world, researchers may face a wide variety of research types, and one may need clarification about finding the right type. Fortunately, you can use a research pyramid to find the best type of study that suits your work. The research pyramid is a model that helps researchers find the best type of study that gives the right answers to their research questions. In addition, the research pyramid can investigate the quality and relevance of the present evidence. This article aims to briefly explain the concept of a research pyramid, its different shapes, and finally, how you can use it to select the best type of study for your research.

What is exactly a research pyramid?

As mentioned above, the research pyramid is a model, and it is designed based on the following principles:

  1. Not all types of evidence are equal
  2. Some kinds of evidence are more reliable and valid than others

The pyramid can distinguish that different kinds of evidence may be more appropriate for different kinds of research questions and purposes.

The pyramid comprises different levels (or layers) of evidence, and these layers are classified from the highest to the lowest based on quality and quantity. The upper layers are the most challenging and reliable studies, while the lower layers relate to easier and less trustworthy ones. In addition, the upper levels of evidence give more comprehensive and synthesized information; on the contrary, the lower layers provide more specific and individualized data.

Different shapes of the research pyramid

As explained earlier, a research pyramid has different versions based on the field of study. However, the most common versions are as follows:

Systematic reviews and meta-analysis

Systematic reviews and meta-analyses collect, assess and synthesize the outcome of different primary studies regarding a particular topic or question. They utilize transparent methods and techniques to decrease bias and errors and give an overall estimate of the effect or relation of an intervention or exposure. This type has the highest level of evidence since they give the most comprehensive and reliable summary of the existing evidence. Systematic reviews and meta-analyses are based on the quality and availability of the preliminary studies, so they may only be usable for some disciplines or populations.

Randomized controlled trials (RCTs)

In these types of studies, participants are categorized into two or more groups and receive interventions or exposures; the researcher compares their outcomes to see if there are any significant differences. Such trials have gold standards to assess the effectiveness of the influence of interventions or exposures. RCTs can minimize confounding and selection bias using randomization. It is worth mentioning that such studies may face different limitations, including ethical issues, feasibility issues, generalizability problems, and methodological defects.

Cohort studies

The prominent characteristic of cohort studies is that they follow participants with different exposure during a specific period and finally compare their outcomes. These studies are a helpful tool for investigating the influence of exposure or risk factors on health. Researchers specifically use Cohort studies when randomized controlled trials are not feasible or have ethical issues. However, similar to any study, cohort studies have limitations regarding confounding bias, selection bias, measuring bias, and follow-up loss.

Case-control studies

In this type of study, participants are selected depending on their outcome status, i.e., cases or controls, and their exposure status compared retrospectively. These types of studies are valuable for evaluating rate outcomes or outcomes with long latency periods owing to the fact that they need a low number of participants and, thereby, need less time than cohort studies. On the contrary, they may face limitations like recall bias, selection bias, measurement bias, and reverse causation.

Cross-sectional studies

Cross-sectional studies can measure the exposure and outcome status of enrolled at a single time point. So, these are perfect for describing the prevalence or distribution of exposures or outcomes in a population. Additionally, Cross-sectional studies are valuable tools to generate hypotheses for further research based on the results of the provenance or distribution of the study subject. Alongside their valuable function, they have some limitations, including confounding bias, measurement bias, and incapability to determine temporal sequence or causality.

Case series and case reports

These kinds of studies can explain the features and outcomes of one or a low number of participants with a specific exposure o outcome. Case series and case reports came in handy in identifying new phenomena or uncommon events to depict clinical practice. However, such studies suffer from limitations such as lack of comparison group, inability to generalization, inability to control confounding factors, or lack of statistical analysis.

How can a research pyramid help researchers to select the best type of study

After explaining the different shapes of research pyramids, its time to describe how to use them to select the best type of study for our research question or purpose. To find how you can consider the following factors:

The type of question

Typically, different types of questions need different kinds of evidence. For instance, a question of research regarding the effectiveness or efficiency of a new drug for cancer therapy may need RCTs or systematic reviews, while questions about prognosis or predicting the possibility of heart attack occurrences in people with blood pressure require cohort studies. On the contrary, questions regarding the etiology of brain stroke in teenagers may require case-control studies. In a similar fashion, questions about the diagnosis of a specific disease may need cross-sectional studies. In contrast, questions about the description of the same disease may require case series or case reports.

The level of evidence

As mentioned earlier, the higher layers of evidence have more reliable and valid data than the lower layers. So, you, as a researcher, should utilize the upper layers of evidence available for your study question or purpose. However, you should be fully aware of the quality of individual studies among each level of evidence since all studies within a layer may not be quite good or usable.

The validity of the evidence

The upper layers of the research pyramid may only sometimes be available for each question or purpose. So, as a researcher, you must search for and utilize the best available option for your goal, even if it is not high-level evidence. You should also know entirely about the limitations and uncertainty of lower layers of evidence.


The research pyramid is a valuable model that helps researchers to select the best type of studies based on their goals and, at the same time, evaluate the quality and relevance of the available evidence. It is mainly based on these facts that all types of evidence are not equal, and some are more reliable than others. It can help researchers to select the best study for their purpose based on the question type, evidence layer, and the availability of evidence.

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