This topic provides an introduction to evidence-based practice and research in wound care.
TYPES OF CLINICAL STUDIES
Table 1 lists different types of clinical studies and their descriptions.
Table 1. Different types of clinical studies according to NICE/UK [3][4]
| Type of clinical study | Description |
| Meta-analysis | A statistical technique for combining (pooling) the results of a number of studies that address the same question and report on the same outcomes to produce a summary result. The aim is to derive more precise and clear information from a large data pool. It is generally more likely to reliably confirm or refute a hypothesis than the individual trials
|
Randomized controlled trial (RCT)
| A comparative study in which participants are randomly allocated to intervention and control groups and followed up to examine differences in outcomes between the groups
|
Cohort study
| A retrospective or prospective follow-up study. People to be followed up are grouped on the basis of whether or not they have been exposed to a suspected risk factor or intervention. A cohort study can be comparative, in which case two or more groups are selected on the basis of differences in their exposure to the intervention of interest.
|
Prospective cohort study
| An observational study that takes a group (cohort) of patients and follows their progress over time in order to measure outcomes such as disease or mortality rates and make comparisons according to the treatments or interventions that patients received. Prospective cohorts are assembled in the present and followed into the future
|
Cross-sectional study
| The observation of a defined set of people at a single point in time or time period. This type of study contrasts with a longitudinal study, which follows a set of people over a period of time
|
Observational study
| Retrospective or prospective study in which the investigator observes the natural course of events with or without control groups (for example, cohort studies and case-control studies)
|
Case-control study
| Comparative observational study in which the investigator selects people who have experienced an event (for example, developed a disease) and others who have not (controls), and then collects data to determine previous exposure to a possible cause
|
Case series
| Report of a number of cases of a given disease, usually covering the course of the disease and the response to treatment. There is no comparison (control) group of patients
|
Case report
| Report of one or two of cases of a given disease, usually covering the course of the disease and the response to treatment. There is no comparison (control) group of patients |
LEVELS OF EVIDENCE
A cornerstone of evidence-based practice is the hierarchical system of classifying evidence. Different types of evidence are available and their relative importance for changing clinical practice has been organized into a hierarchy.[3]
The levels of evidence were originally described in a report by the Canadian Task Force in 1979 (Table 2).[5] Since the introduction of levels of evidence, many other organizations have developed a variation of the original classification system. [6] As a result, clinical practice guidelines have been inconsistent in how they rate the quality of evidence and the strength of recommendations.[2]
Table 2. Canadian Task Force on the Periodic Health Examination’s Levels of Evidence [5][6]
| Level | Type of evidence |
| I | At least 1 RCT with proper randomization
|
| II.1 | Well designed cohort or case-control study
|
| II.2 | Time series comparisons or dramatic results from uncontrolled studies
|
| III | Expert opinions
|
GRADE APPROACH
The Grading of Recommendations Assessment, Development and Evaluation (short GRADE) is a systematic approach to rating the certainty of evidence in systematic reviews and other evidence syntheses. [7] The GRADE working group began in the year 2000 as an informal collaboration of people with an interest in addressing the shortcomings of grading systems in health care. The working group has developed a common, sensible and transparent approach to grading quality (or certainty) of evidence and strength of recommendations. Many international organizations have provided input into the development of the GRADE approach which is now considered the standard in guideline development, utilized by over 100 organizations worldwide [7], including WoundReference.
What makes a good grading system?
Several grading systems have been used by guideline authors. However, not all grading systems separate decisions regarding the quality of evidence from strength of recommendations.[2] This may result in confusion, as high quality evidence does not necessarily imply strong recommendations, and low quality evidence can lead to strong recommendations. Grading systems that are simple with respect to judgments both about the quality of the evidence and the strength of recommendations facilitate use by patients, clinicians, and policy makers.[2]
How does the GRADE system classify quality of evidence?
The GRADE system classifies quality of evidence in one of four levels: high, moderate, low, and very low (Table 3).[2]
Table 3. GRADE certainty ratings [8]
| Certainty | Description |
| High | The authors have a lot of confidence that the true effect is similar to the estimated effect |
| Moderate | The authors believe that the true effect is probably close to the estimated effect
|
| Low | The true effect might be markedly different from the estimated effect
|
| Very low | The true effect is probably markedly different from the estimated effect |
- Evidence based on RCTs begins as high quality evidence, but confidence in the evidence may be decreased for several reasons, including [2]:
- Study limitations
- Inconsistency of results
- Indirectness of evidence
- Imprecision
- Reporting bias
- Although observational studies (e.g. cohort and case-control studies) start with a “low certainty” rating, grading upwards may be warranted if the magnitude of the treatment effect is very large, if there is evidence of a dose-response relation or if all plausible biases would decrease the magnitude of an apparent treatment effect.[2]
For more information on the GRADE approach, please refer to resources on Grade Working Group, Cochrane.org and BMJ Best Practice.
