A Guide to Study Designs in Physiotherapy Research
Physiotherapists rely on research to inform their own practice in evidence-based medicine (1). Evidence-based medicine is defined as the combination of research, clinical expertise, and patient values to guide decision-making in the care of patients.
In order to practice the research component of evidence-based medicine, physiotherapists must stay up-to-date on the vast body of scientific literature. They must also understand the hierarchy of study designs and how they are represented in physiotherapy research.
Here we will break down the different study designs you will find in physiotherapy research. For each study design, we will discuss scenarios in which they are used, as well as provide examples in physiotherapy research.
Randomized Controlled Trials
Randomized controlled trials are the highest level of research design, often considered the “gold standard” for determining effectiveness of a new treatment (2). They are prospective, meaning they are planned before any data collection occurs. They involve the random assignment of participants into an experimental or a control group.
Specific to physiotherapy research, the control group will often receive some kind of therapy, instead of no therapy like a true control group. For example, here is a randomized controlled trial that compared supervised resistance training to home-based resistance training (rather than no training) for patients with subacromial shoulder pain.
Randomization creates an equal opportunity for participants to be in either group. This reduces bias by balancing participant characteristics between the groups. Oftentimes, participants don’t know to which group they are assigned (also known as “blinding”).
Randomized controlled trials are the best way to determine causation (i.e. outcomes due to the intervention rather than other factors).
Cohort studies follow participants who share a common characteristic. They are longitudinal, meaning researchers observe participants for a certain period of time. They can be prospective (following participants forward in time) or retrospective (following participants back in time).
Cohort studies are best for determining the external factors that influence health. They also help determine risk factors for injuries or conditions.
In physiotherapy, researchers could use a cohort study to follow patients who have undergone physiotherapy treatment for a specific condition. All participants received the treatment and were not randomly assigned like in a randomized controlled trial. Researchers determine if factors (such as age, injury severity, compliance to therapy, etc.) affect outcomes of the treatment. This research review by Dr Mariana Wingwood provides an example of a retrospective cohort study that evaluated early rehab on function in patients with vertebral compression fractures.
Prospective cohort studies are a strong study design and quite common in physiotherapy research. Another review by Stacey Harden is an example of a prospective cohort study that followed professional football (soccer) players to evaluate risk factors for hip and groin pain which you can find here.
Case-control studies are studies that look back in time to compare patients who have an injury/condition (cases) to patients who do not have injury/condition (controls). The controls are usually matched to the cases on several demographic variables, such as age, sex, and physical activity status.
Case-control studies are helpful in determining risk factors for injuries or conditions. Many researchers will conduct them as an initial study to learn more about an injury/condition prior to conducting a prospective trial.
Case-control studies are common in physiotherapy, such as this research review by Dr Melinda Smith on the investigation of risk factors in runners with medial tibial stress syndrome compared to matched asymptomatic runners.
Cross-sectional studies are observational studies that evaluate data from participants at a single time point. They are used to determine associations between two variables. For example, this research review by Steve Kamper used a cross-sectional design to determine if posture and smartphone use were related to neck pain in young adults.
Physiotherapy researchers use cross-sectional studies for survey-based research, as well as clinical-based studies. Cross-sectional studies are usually more time and cost effective, and are therefore more appealing and tangible in physiotherapy clinical settings.
Case Series and Case Studies
The last and weakest study designs are case series (~<10 people in a study) and case studies (1 person in a study). They are considered the weakest of study designs because due to the small sample size, they are less likely to be generalizable to the population of interest.
However, case series/studies can be extremely informative to physiotherapy practice, as they usually describe rare or unusual injuries or conditions. They provide a glimpse into the clinical practice of another therapist and healthcare team, which can help inform your own practice. An example you can find here was reviewed by Robin Kerr in a case series of 5 patients who underwent an alternative treatment approach for frozen shoulder.
In practicing evidence-based medicine, it is important to be familiar with the different study designs that can be found in physiotherapy research. Understanding the indications for each study design will aid physiotherapists in determining if the study should affect or change their clinical practice.
Keep in mind that each type of study has its advantages and disadvantages. Although they are ordered in a hierarchy of strongest (i.e., randomized controlled trials) to weakest (i.e., case studies) design, we have covered some considerations specific to physiotherapy research that make certain designs more common and efficient than others.
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- Manchikanti L, Boswell MV, Giordano J. Evidence-based interventional pain management: principles, problems, potential and applications. Pain Physician. 2007 Mar;10(2):329-56. PMID: 17387356.
- Hariton E, Locascio JJ. Randomised controlled trials – the gold standard for effectiveness research: Study design: randomised controlled trials. BJOG. 2018;125(13):1716. doi:10.1111/1471-0528.15199.
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