Evidence · how to read it

Reading the
evidence

Which study do I trust first?

Not all evidence carries the same weight. Before you carry a finding onto a shift, it helps to read it on a few simple scales — a guide for weighing the literature, not a verdict.

The Ladder

What kind of study is it?

The Meter

How sure are we of the answer?

The Scope

Is it your call to act on?

The Ladder · Oxford level of evidencetap a rung

Reading the codenumber = the kind of study · letter = how many

The number is what kind of study it was — and how much that kind can be trusted. 1 is the strongest kind: a fair experiment where a coin-flip decides who gets the treatment, so the groups start out even. 5 is the weakest: an expert's opinion, with no study behind it. The letter tells you how many — a = many studies of that kind, gathered and combined; b = a single study.

◓ A review (1a · 2a · 3a) reads all the rungs below it — not just the top brick.

The rungs are a guide, not a verdict — a strong study of one kind can outweigh a weak one a rung above.

The Meter · GRADE certaintyhow sure?

High

Very confident; more research is very unlikely to change the answer.

Moderate

Fairly confident; knocked down a notch — e.g. the studies didn't fully agree.

Low

Limited confidence; typical of observational studies or trials with weaknesses.

Very Low

Very little confidence; serious problems, or very thin evidence.

n/a — no comparative grade. When the library holds no comparative evidence for a question, it says so, rather than inventing a grade.

The Scope · your roleyour call?

Core — manage36 topics

Within the fellow's scope to manage directly.

Shared — co-manage47 topics

Managed together with the attending.

Attending-led — refer59 topics

Recognize it, then refer or escalate.

Background — be aware2 topics

Know it exists; not a primary management target.

Go deeper · interactive

The numbers inside a study.

Quick definitionsWhat the acronyms mean — RCT, N, standard deviation, p-value — one plain sentence each.→ Walk through a real studyA guided, visual course — see how a study is judged, step by step. (Its own page; video coming.)→

Everything here is interactive — tap a rung, open a study, explore. This page is the study tool, not a page about one.

References

OCEBM Levels of Evidence Working Group. (2011). The Oxford 2011 levels of evidence. Oxford Centre for Evidence-Based Medicine. https://www.cebm.ox.ac.uk/resources/levels-of-evidence/ocebm-levels-of-evidence

Schünemann, H., Brożek, J., Guyatt, G., & Oxman, A. (Eds.). (2013). GRADE handbook for grading quality of evidence and strength of recommendations. The GRADE Working Group. https://gradepro.org/handbook/