Levels of Evidence Codes

LEVELS OF EVIDENCE

“Helen of Troy”, (Dianne Kruger, in “Troy”, Warner Bros 2004)

I thought love was only true in fairy tales
Meant for someone else but not for me.
Oh, love was out to get me
That’s the way it seems
Disappointment haunted all my dreams.
Then I saw her face…

…Now I’m a believer!

“I’m a Believer”, The Monkees 1966.

Helen of Troy was the most beautiful woman of the ancient classical world, so beautiful in fact she was the cause of the most protracted and devastating conflict of that age. Tens of thousands on both sides would die over the ensuing ten year war that followed Paris’ abduction of her from Greece and ended only with the total destruction of the city of Troy.

The story of the Trojan War is deeply ingrained in the Western consciousness, influencing its thought, culture, traditions and heritage for millennia. Always assumed to be myth the Western world was electrified in 1870 by an eccentric German archeologist by the name of Heinrich Schliemann who claimed to have uncovered the ruins of the city of Troy in northwestern Turkey.

Whether these ruins truly represent the ancient Troy of Homer’s Iliad is open to debate, but there nonetheless remains intriguing and compelling arguments that it is. It all depends on how one chooses to view the evidence. For some the evidence is simply not “hard” enough, yet for many of more romantic disposition there is no doubt in their mind that the ruins truly are those of ancient Illium.

The whole story says much of human nature, the deeply ingrained even primal dichotomy of heart versus mind. To launch the most devastating conflict of the Bronze Age was a momentous decision, one would have thought that all the evidence for and against war was carefully weighed before the final decision to attack was made. Agamemnon attempted to do this by considering the economic advantages for Greece of the total destruction of Troy. He used level 1 evidence to help make his decision. However in the end it was the level 4 “expert” opinion of Paris, that decided the issue in the minds of most of the Greek Kings. Economic advantage may be terribly “sensible” but when it comes to matters of the heart “sense” will very often loose out.

All men (and many women) since the time of Troy have wondered to themselves “just how beautiful must Helen of Troy have been?” Since the time of Homer the only evidence we had available to us was the level 4 “expert” opinion of Homer himself. However early in the Seventeenth century a certain Dr. Faustus sold his soul to the Devil and among other compensations for this he requested to see the face of Helen of Troy, where upon the Devil immediately bought forth her image.

Faustus thus becoming our only other historical source for confirmation of Helen’s beauty. Christopher Marlow left an account to history of Faustus’ awestruck reaction upon gazing into her face:

“…Was this the face that Launcht a thousand ships,
And burnt the toplesse Towers of Ilium?
Sweet Hellen make me immortall with a kisse…”

…I will be Paris, and for love of thee,
In stead of Troy shall Wittenberg be sack’t…

…Yea, I will wound Achilles in the heel

And then return to Helen for a kiss…”

The Tragicall Historie of the Life and Death of Doctor Faustus, Act V, scene1 Christopher Marlow, 1616.

Thus the evidence for Helen’s beauty raised itself from a WHO level 4 to WHO level 3 upon the corroborating evidence of Dr Faustus in 1616. In 1870 the “quasi” scientific researches of Heinrich Schliemann raised it again to a level IIB upon his discovery of the more “scientific” based evidence for the real existence of Troy.

In the 21st century we like to pride ourselves on our scientific rationality. In the field of medicine we now strive for the “evidence base” in everything that we do, before we make any “momentous” decisions, yet is this a realistic or even entirely desirable thing in all cases? Paris knew a “good sort” when he saw one and that was enough for him and for the rest of the Greek city-states to follow him into battle.

LEVELS OF EVIDENCE

NHMRC Levels of Evidence Codes1

E1Level 1

Evidence obtained from a systematic review of all relevant randomised controlled trials.

E2Level 2

Evidence obtained from at least one properly designed randomised controlled trial.

E31Level III-1

Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method)

E32Level III-2

Evidence obtained from comparative studies with concurrent controls and allocation not randomised (cohort studies) case-control studies, or interrupted time series without a parallel control group.

E33Level III-3

Evidence obtained from comparative studies with historical control, two or more single arm studies, or interrupted time series without a parallel control group.

E4Level IV

Evidence obtained from case-series, either post test or pretest and post test.

Grade of Recommendation Description2

NHMRC grades of recommendation are provided to assist users of the clinical practice guideline in making clinical judgements and indicate the strength of the recommendation.

Grade A and B recommendations are generally based on a body of evidence which can be trusted to guide clinical practice, whereas Grade C and D recommendations must be applied carefully to individual clinical and organisational circumstances and should be followed with care.

A Body of evidence can be trusted to guide practice

BBody of evidence can be trusted to guide practice in most situations

C Body of evidence provides some support for recommendation(s) but care should be taken in its application

DBody of evidence is weak and recommendation must be applied with caution

WHO (World Health Organization) categories of evidence3

1 AEvidence from meta-analysis of randomised controlled trials.

1 BEvidence from at least one randomised controlled trial.

II AEvidence from at least one controlled study without randomisation.

II BEvidence from at least one other type of quasi-experimental study.

IIIEvidence from non-experimental descriptive studies, such as comparative studies, correlation studies and case-control studies.

IVExpert opinion.

World Health Organization strength of recommendations

ADirectly based on category I evidence.

BDirectly based on category II evidence or extrapolated recommendation from category I evidence.

CDirectly based on category III evidence or extrapolated recommendation from category I or II evidence.

DDirectly based on category IV evidence or extrapolated recommendation from category I, II or III evidence.

ILCOR & American Heart Association 2005 Levels of Evidence4

Level 1Randomized clinical trials or meta-analysis of multiple clinical trials with substantial treatment effects.

Level 2Randomized clinical trialswith smaller or lesssignificant treatment effects.

Level 3Prospective, controlled, non randomized cohort studies.

Level 4Historic, non randomized cohort or case control studies.

Level 5Case series, patients compiled in serial fashion, control group lacking.

Level 6Animal studies or mechanical models.

Level 7Extrapolations from existing data collected for other purposes, theoretical analyses.

Level 8Rational conjecture (common sense), common practices accepted before evidence-based guidelines.

References

1NHMRC, A guide to the development, implementation and evaluation of clinical practice guidelines. Canberra 1999.

2NHMRC Additional levels of evidence and grades for recommendations for developers of guidelines. Pilot Program 2005-2007

3WHO Guidelines in, MJA vol 182 (9) 2 May 2005, p.465.

4AHA 2005 Guidelines for Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care (ECC). Circulation, December 13, 2005.

March 2007