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Evidence-based Practice (EBP)

Answer basic questions to improve your practice.

Primary Studies- Study Designs

Different types of clinical questions are best answered by different types of research study designs. Often, you may not find the highest level of evidence (eg: systematic review or clinical practice guideline) to answer your research question. In such a scenario, you will have to look through the next available evidence.

 Source: NSW Ministry of Health, CIAP

This page is designed to help you:

  • Understand different types of studies and how they are used in the clinical research
  • Ability to locate articles based on different study types 
  • Glossary of terms related to clinical studies
Which Study type?

The clinical research question covers a variety of topics like diagnostic accuracy, prognosis, screening, intervention, causation etc. Each of these questions has its own best study type that gives the best evidence. 

Begin by thinking about what field your clinical question falls under. 

Question Type Best Research Design
Therapy or Intervention Randomized controlled trial (RCT)
Aetiology or Causation Cohort study , Randomized controlled trial (RCT)
Diagnosis Randomized controlled trial (RCT) , Cohort study 
Prognosis Cohort Study or Case-Control Series
Prevention Randomized controlled trial (RCT) or Prospective Study
Meaning Qualitative study
Quality improvement Randomized controlled trial (RCT) 
Cost Economic Evaluation
Randomised Controlled Trial (RCT)

RCTs are carefully planned experiment that studies the effect of an intervention (eg: drug) or therapy on real patients against another group( placebo or different therapy). The methodologies include randomisation and blinding which reduce bias and comparison between groups. The only expected difference between the control and experimental groups in RCT is the outcome variable being studied.

Example Report

van der Horst, N., Smits, D. W., Petersen, J., Goedhart, E. A., & Backx, F. J. (2015). The preventive effect of the nordic hamstring exercise on hamstring injuries in amateur soccer players: a randomized controlled trial. The American journal of sports medicine43(6), 1316–1323.

Cohort Study

Study design where one or more samples with a particular condition or receiving particular treatment, called cohorts, are followed prospectively and compared with another group who have not been affected by the condition or treatment being studied.

Not as reliable as RCT since the two groups might differ in ways (confounding variables) other than the variable being studied. Also, this study design does not involve randomization, which means imbalances in patient characteristics could exist.

Example Report

Lee, Y. G., Chang, Y., Kang, J., Koo, D. H., Lee, S. S., Ryu, S., & Oh, S. (2019). Risk factors for incident anemia of chronic diseases: A cohort study. PloS one14(5), e0216062.

Case-Control Study

A study in which people who have a disease or outcome of interest (cases) are compared with those who do not. The researcher looks back retrospectively to identify risk factors that might be associated with the condition. Often relies on medical data or patient recall. Case-control studies are observational because no intervention is involved and no attempt is made to change the course of the disease. However, case-control studies are less reliable than an RCT or cohort study because cause and effect are not necessarily established.

Example Report

Boubekri, M., Cheung, I. N., Reid, K. J., Wang, C. H., & Zee, P. C. (2014). Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine10(6), 603–611.

Cross-Sectional Study

A study in which a disease or a medical condition and associated factors are measured at a specific point in time for a given population. The cross-sectional study design is a type of observational study design.

Cross-sectional studies are :

  • used for estimating the prevalence in clinic-based studies
  • classified as descriptive or analytical

Case Report / Case Study/ Case Series

A report on the treatment of an individual patient or case. There is no statistical validity as there is no control group for comparison. Where there are a number of case reports, this is known as a case series.

Case reports often include:

  • A unique case that cannot be explained by known diseases
  • cases show a significant variation of a disease or medical condition
  • cases involve unexpected events which may lead to new information

Example Report

Patial, T., Chaddha, S., Rathore, N., & Thakur, V. (2017). Small Bowel Volvulus: A Case Report. Cureus, 9(5), e1281.

Systematic Reviews versus Primary Studies: What's Best?

A well done Systematic review, with or without meta-analysis is often considered as the best evidence for answering all kinds of research questions. However, considering systematic review as the best evidence is not always absolute. As such,

  • The methodical rigour and strength of findings must be appraised before applying.
  • A Systematic review may have superseded some of the recent publications due to the rigour and study duration.