levels of evidence in physical therapy
Anyone out there who knows me, knows one thing about me. I love generalizing, and I already know it, it does not work in my favor. I am the type of guy who would tell you that “everyone who does weightlifting is strong” (which is true!). Also I often say things like “all guys like eating salty stuff, and all girls like eating sweet stuff” (yes, I know this is not always the case).
Sound familiar? Let me point out a few specific examples in the fitness and physical therapy fields that may seem familiar to you. A new supplement that promises to turn each pound of body fat into a pound of muscle in less than a week. A new workout that will make you the best weightlifter in the world in less than a year. A new physical therapy modality that will promote the growth of your meniscus after you twisted your knee and tore the meniscus. The examples are endless and it is not uncommon that we are mislead by an “expert”/company for purely for the purpose of them getting our money.
As a physical therapy professional I am responsible for applying current research findings at work. This helps me to effectively treat my patients/clients as well as to educate other health care professionals and the general public about research findings that are meaningful to the field of physical therapy.
The real question is what research is “meaningful” in the fields of physical therapy and fitness? To answer this question we have to look at the hierarchy of “levels of evidence”. As a therapist I consider the highest level in the hierarchy to be the most useful to look at because they are ranked according to the strength of the research design. Simply put, the higher the research design, the more evidence there is to answer the specific question that is asked in the research study. We must be aware that as the level of evidence decreases, the strength of evidence decreases.
Here is a quick breakdown of the levels of evidence from the lowest level to the highest level:
Ideas/Opinions = are not more than that, be careful in even taking them into consideration.
Case report = as the name suggests, these are based only on one specific individual patient/client.
Case series = based on several cases that are mostly similar in nature (Glossary of Statistical Terms. Centre for Evidence-Based Medicine Web site. http://www.cebm.net/glossary/. Accessed June 27, 2015).
Cross-sectional study = in this kind of study the data is collected at only one point in time and all subjects are tested at the same time. This shows the relationship between a disease and factors that exist in the specified population (Roy S, Wolf S, Scalzitti D. The Rehabilitation Specialist’s Handbook. Forth Edition, F.A. Davis Company. 2013).
Case control study = in this type of study, people with a condition are compared to people without the condition. This way the study can estimate what kind of exposure is significant to people with the condition, compared to people without the condition (Glossary of Statistical Terms. Centre for Evidence-Based Medicine Web site. http://www.cebm.net/glossary/. Accessed June 27, 2015).
Cohort study = an observational study that follows people with a risk factor or exposure over time to compare the occurrence of disease in the exposed group to the unexposed group (Glossary of Statistical Terms. Centre for Evidence-Based Medicine Web site. http://www.cebm.net/glossary/. Accessed June 27, 2015).
Randomized controlled trial = experimental research that examines the effect of an intervention compared to a control condition. This research assigns people with the same conditions to two groups, one that receives no treatment or basic treatment, compared to a second group that receives the specific treatment (Guidelines by Topic. National Guideline Clearinghouse Web site.http://www.guideline.gov/. Accessed June 27, 2015).
Meta-analysis = comprehensive review that uses statistics to derive an estimate of effect size by combining the results of several randomized controlled trails to determine the overall effectiveness of the treatment. Since the information is gathered from several studies, this type of evidence is considered to be very valuable and should be used most often to derive answers to clinical questions (Glossary of Statistical Terms. Centre for Evidence-Based Medicine Web site. http://www.cebm.net/glossary/. Accessed June 27, 2015).
Systemic review = comprehensive review of medical literature. Just like Meta-analysis, this type of evidence is considered to be very valuable since it summarizes all of the literature on a specific issue. (Sackett DL, Straus SE, Richardson WS, Rosenburg W, Haynes RB. Evidence-Based Medicine. How to Practice and Teach EBM. 2nd ed. Edinburgh, Scotland; Churchill Livingstone. 2000).
Research is becoming very prevalent in the field of physical therapy, as well as in the field of fitness - especially strength and conditioning. Adhering to these rules of levels of evidence in practice will help you be an expert in the field. Also it will help you avoid buying that future hundred thousand dollar treadmill that promises to help build your leg strength by keeping you up in the air.