Importance Of Levels Of Evidence In Systematic Review

Levels Of Evidence

Level of evidence refers to the strength of a piece of research. How good is the study? What are its limitations? Each level has its own strengths and weaknesses, which you can use to decide how much weight to give it in your work. In a systematic review, the strength of evidence is determined by the type and quality of clinical studies that were conducted. There are four levels of evidence in medical research:

  • Randomized controlled trials (RCTs)
  • Non-randomized controlled trials (non-RCTs)
  • Case-control studies
  • Cohort studies (longitudinal cohort studies are considered to be level III evidence)

The best type of study is a randomized controlled trial because it’s the most objective and allows researchers to control all variables that may affect their results. However, there are some situations where this isn’t possible (such as testing new medications on human subjects). In these cases, researchers use other types of studies such as case-control or cohort studies; however, these types of research cannot provide definitive evidence about cause-and-effect relationships between two things because they’re not randomized experiments. In this article, experts of The Academic Papers UK will explore different levels of evidence in a systematic review

Definition of Levels of Evidence

In systematic reviews and meta-analyses, the level of evidence associated with a type of study is used to determine how reliable the results of that study are. For example, if you were conducting a systematic review about the risk for stroke after angioplasty (a procedure to open up blocked arteries in the heart), it would be important for your review to include studies that had high levels of evidence.

This is because only studies with high levels of evidence can give you a strong conclusion about whether or not there really is an increased risk for stroke after angioplasty. Studies with low levels of evidence might not be able to accurately answer this question because they may have too many biases or flaws in their design and implementation.

It’s also important that all studies included in your systematic review have similar levels; otherwise, it will be harder for readers to interpret your conclusions because some studies’ results may appear stronger than others’.

Level I: Evidence Obtained From One Or More Well-Designed Randomized Controlled Trials

A controlled trial is an experimental study that assesses the impact of an intervention on health outcomes (e.g., mortality, morbidity) or other effects (e.g., quality of life). In these studies, participants are randomly assigned to one group or another so that each has an equal chance of receiving either the intervention being studied or a control treatment (such as placebo). The results from these experiments can be used to determine whether there was actually any difference between the two groups and, therefore, whether there is evidence supporting the effectiveness of a particular treatment.

Level II: Evidence Obtained From One Or More Well-Designed Non-Randomized Controlled Trials

A quasi-experimental study or non-randomized controlled study is a type of observational study that is similar to an experimental study but differs in that the participants are not randomly assigned to the intervention or control group. Quasi-experiments may be used when it is impossible or unethical to randomly assign participants; for example, if you want to evaluate the effectiveness of a new vaccine, you would use a quasi-experimental design because it’s unethical to randomly assign some people not receive the vaccine against their will (although trials have been conducted with children). If you are also planning to conduct Quasi-experimental study in your dissertation but do not have the right expertise, then get assistance from experts of master dissertation help.

In addition, there are times when an experiment cannot be easily replicated due to changes in population characteristics or other factors. For example, say you wanted to evaluate whether an increase in public transportation had resulted in less traffic congestion during peak hours near major cities—you could use this data as your sample pool if someone else did not already have access to it (which is unlikely).

Level III: Evidence Obtained From Well-Designed Non-Experimental Descriptive Studies, Such As Comparative Studies, Correlation Studies And Case Studies

A study is classified into level III if it does not involve a control or comparison group, or if the outcome of interest was measured pre- and postintervention. The strength of association between an intervention and an outcome in a correlational study is often presented as a simple correlation coefficient r. The strength of association can also be measured by other indices such as chi-square test statistic. These types of studies are useful for generating hypotheses but cannot prove causation, so they are considered weak forms of evidence compared with systematic reviews that use only randomized clinical trials (RCTs) or cohort studies as sources of data on effectiveness.

Level IV: Evidence Obtained From Expert Committee Reports Or Opinions And/Or Clinical Experiences Of Respected Authorities (Cohort Studies)

This type of evidence can be useful to help determine the overall effectiveness of interventions but should not be used alone to determine if an intervention works or not. This type of evidence is often found in systematic reviews, especially when the review is focused on a specific topic (e.g., “Does yoga work for cancer patients?”). Expert committee reports are also considered level 4 evidence because they are based on the opinions of experts who may have been funded by pharmaceutical companies (they might have been paid to write a report that says something worked).

Clinical experience refers to how well you think something works by looking at your own patients; this information is always biased toward what worked for them and can’t be generalized across different patient populations or situations.


In summary, the evidence-based practice uses the best available evidence to make health care decisions. The strength of this type of decision-making is dependent on the quality and level of evidence that supports it. We hope this article has helped you understand how levels of evidence can be used in systematic reviews and why it’s important for your own practice.


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