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Nutrition

Resources for students and faculty in the Department of Nutritional Sciences.

Levels of Evidence

Levels of evidence are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. The combination of these attributes gives the level of evidence for a study.  In nursing, the system for assigning levels of evidence is often from Melnyk & Fineout-Overholt's 2011 book, Evidence-based Practice in Nursing and Healthcare: A Guide to Best Practice.  The Levels of Evidence below are adapted from Melnyk & Fineout-Overholt's (2011) model. 

Levels of Evidence chart: Level I: Evidence from a systematic review of all relevant randomized controlled trials (RCT's), or evidence-based clinical practice guidelines based on systematic reviews of RCT's. Level II: Evidence obtained from at least one well-designed Randomized Controlled Trial (RCT). Level III: Evidence obtained from well-designed controlled trials without randomization, quasi-experimental. Level IV: Evidence from well-designed case-control and cohort studies. Level V: Evidence from systematic reviews of descriptive and qualitative studies. Level VI: Evidence from a single descriptive or qualitative study. Level VII: Evidence from the opinion of authorities and/or reports of expert committees

About Levels of Evidence and the Hierarchy of Evidence: While Levels of Evidence correlate roughly with the hierarchy of evidence (discussed elsewhere on this page), levels of evidence don't always match the categories from the Hierarchy of Evidence, reflecting the fact that study design alone doesn't guarantee good evidence. 

About Levels of Evidence and Strength of Recommendation: The fact that a study is located lower on the Hierarchy of Evidence does not necessarily mean that the strength of recommendation made from that and other studies is low--if evidence is consistent across studies on a topic and/or very compelling, strong recommendations can be made from evidence found in studies with lower levels of evidence, and study types located at the bottom of the Hierarchy of Evidence. In other words, strong recommendations can be made from lower levels of evidence.

For example: a case series observed in 1961 in which two physicians who noted a high incidence (approximately 20%) of children born with birth defects to mothers taking thalidomide resulted in very strong recommendations against the prescription and eventually, manufacture and marketing of thalidomide. In other words, as a result of the case series, a strong recommendation was made from a study that was in one of the lowest positions on the hierarchy of evidence.

Additional Evaluation Resources

Structuring Research Questions

The PICO format is used in healthcare to help construct research questions used in systematic reviews

P= Patient, Population, Problem

I= Intervention

C= Comparison

O= Outcomes

 

RQ: What is the best diet for patients who have high blood pressure to prevent future heart attacks?

P= Patients with high blood pressure

I= Low sodium diet

C= Low fat diet

O= Heart attack prevention

 

How to search this in a general database:

"high blood pressure" AND ("low sodium diet" OR "low fat diet") AND "heart attack"

 

Other ways to breakdown or construct research questions

BeHEMoTh - identification of theories for realist synthesis questions

B Behaviour of interest
H Health context (the service, policy, program or intervention)
E Exclusions (for reviewers to exclude non theories)
MoTh: Models or Theories
 

CLIP –Health service management questions

C Client – at whom is the service aimed?
L Location – where is the service sited?
I Improvement – what do you want to find out?
P Professional – who is involved in providing/improving the service?

 

ECLIPS(E) – Health service management questions

E Expectation—what does the search requester want the information for?
C Client Group.
L Location.
I Impact—what is the change in the service, if any, which is being looked for? What would constitute success? How is this being measured?
P Professionals.
S Service—for which service are you looking for information? For example, outpatient services, nurse-led clinics, intermediate care.
 

MIP – Medical ethics questions

M Methodology  e.g. in-depth interviews or questionnaires
I Issues e.g. Healthcare Rationing or  end-of-life decision-making
P Participants e.g. physicians or patients

 

SPICE – Social science questions

S Setting – Where? In what context?
P Perspective – For who?
I Intervention (Phenomenon of Interest)– What?
C Comparison – What else?
E Evaluation – How well? What result?

 

SPIDER – Qualitative evidence synthesis

S Sample
PI Phenomenon of Interest
D Design
E Evaluation
R Research type