Using evidence based practice has become linked with problem solving. To be more effective evidence is taken from different sources and there are differing levels of evidence. The levels of evidence are related to the sources of the data or information.

Types of evidence include academic / clinical studies, values / preferances of patients and the experience of medical professionals. Unfortunately there is no universal system for weighting evidence and deciding on the best course of treatment.

Having a strong knowledge of a rating system for evidence allows clinicians to reach better and more consistent decisions on patient treatments as they can weight the value of different reports, studies and evidence from patients.

Rating system

The level rating system presented here has been drawn up with the assistance of nurse practioners. In this system Level A is the strongest evidence and Level C is the weakest level.

Level ML was developed later to fit scenarios when more than 1 level of evidence was needed to reach an evidence based decision.

LEVEL A – where the evidence is obtained from:

This is the most reliable level of evidence as it is Randomized Control Trials (RCT) that set the standard that other forms of evidence to aim to match. Subjects are picked at random and placed into specfic groups at random.

Systematic review of evidence obtained from RCTs – these are reviews of evidence with the aim of answering a specific question using relevant literature and studies too. This approach is a meta-analysis of all the best evidence relating to specific medical cases with certain conditions.

Over all RCTs and systematic reviews are the strongest way to make use of evidence in medical cases.

LEVEL B – where the evidence is obtained from:

Clinical trials without randomization – these studies give less reliable evidence as the subjects are not picked randomly meaning the data and results may not be as useful. The groups in such trials may not be varied so the evidence obtained is not from the widest possible sections of society.

Clinical cohort study – gaining evidence from different groups, to find out if specfic factors have an impact on the development of specific conditions or diseases.

Case control study – comparing the evidence from subjects known to have a specific medical condition to subjects who are not known to have that particular condition. The subjects selected will have similar demographics to make the comparisons of risk factors more realistic. The only difference is that some subjects have the condition and the rest do not.

An Uncontrolled study – this is evidence obtained from subjects that just happened to be in the same place at the same time, for instance all the patients in the same hospital ward on a specific date. This evidence is gained from the only subjects available at that point.

Epidemiological study – evidence obtained from long term observations of people to find out if they develop or have increased risk of conditions. This type of evidence can be obtained from retrospective searches of databases too.

Qualitative or Quantitative study – this is evidence gathered from descriptive word based research, or from recording statistics to find out the impact of various health conditions, or the cause and affect.

LEVEL C – where the evidence is obtained from:

Obtaining a consensus viewpoint and expert opinions of the relevant evidence – by discussing the evidence the aim is to reach an agreement on treatment options. This process is generally used when there is no quality and quantity data yet available about a specific condition. Basically exerts reach agreement by reviewing the limited evidence available.

Meta-synthesis – this is when evidence from various similar studies is put together to come up with a clinical application.

LEVEL ML – where the evidence is obtained from:

The evidence used to make clinical decisions is based on a mix of the levels above. This level uses evidence from various levels as a means of reaching decisions in more complex cases.