The strongest levels of evidence for guiding practice decisions are regarded to be systematic reviews or meta-analyses of randomized controlled trials (RCTs) and evidence-based practice recommendations. These types of studies evaluate all available evidence on a topic and determine how well it supports different practices. The quality of each study contributes to the strength of the evidence.
Other types of evidence may also guide practice decisions, such as observational studies, case series, and expert opinions. Each type of evidence has strengths and limitations that should be considered when making practice decisions.
Systematic reviews or meta-analyses include studies that compare two or more interventions for their effectiveness on a specific outcome. In other words, they examine what works best under real-world conditions. Systematic reviews or meta-analyses can also examine the benefits and harms of an intervention. Finally, they can identify factors that predict who will benefit from an intervention.
Observational studies look at how things are done in practice without randomly assigning patients to different treatments. Observational studies can show whether one treatment is better than another or be used to identify trends in patient care over time. For example, researchers could observe how many patients with diabetes were admitted to hospital over time and then ask them why they went into hospital.
The reason research are arranged in a hierarchy is that those at the top are regarded as having the "best evidence." These are randomized controlled trials (RCTs) and meta-analyses of RCTs in the case of therapeutic trials. Because of the nature of randomization, RCTs have the capacity to assist control bias. Observational studies and expert opinions are considered to be the least reliable forms of evidence.
In conclusion, evidence from well-conducted clinical trials is considered the highest level of evidence. Other types of evidence may provide useful information for making decisions, but cannot replace a trial's findings due to selection and other biases.
Systematic reviews of completed, high-quality randomized controlled trials, such as those published by the Cochrane Collaboration, are typically ranked as the highest quality of evidence above observational studies, while expert opinion and anecdotal experience are at the lowest level of evidence quality.
In conclusion, evidence is information or data that can prove or support the truth of a statement. Evidence is always produced through some kind of observation or experiment. The term "evidence based medicine" refers to the use of the best available evidence to make decisions about the care of individual patients. Best evidence means evidence from well-designed clinical trials that compare different treatments or interventions and measure their benefits and harms. Observational studies and expert opinions are lower down on the evidence hierarchy because they cannot prove or disprove theories about how things work or what is safe and what is not. They can only show association or correlation between something observed after it has happened and something believed to be responsible for the event.
Evidence forms the basis of many important decisions in medical practice. Evidence also helps doctors make recommendations to other physicians or health professionals regarding changes to the management of a patient's condition or the delivery of care.
Both approaches rank randomized controlled trials (RCTs) highest and case studies or expert views lowest. The hierarchies rate research based on the likelihood of bias. RCTs receive the highest rating since they are intended to be unbiased and have a minimal chance of systematic mistakes. Observational studies and experimental studies using animals follow next in order of importance. Case studies provide information on events that cannot be obtained any other way and can give useful insights into causes and effects. Expert opinions are derived from surveys of scholars who review many more papers than those who write them so they are likely to be reliable indicators of the state of research.
Case studies, observational studies, and experimental studies using animals are all considered sub-classes of primary research. Primary research provides evidence that can eventually lead to the development of new therapies or drugs. It may also include studies conducted for purposes other than producing knowledge about human behavior or health but which are relevant to these topics e.g., studies of brains or genes of people with and without schizophrenia. Secondary research uses data collected for other purposes to extend our understanding of phenomena or fill gaps in our knowledge. For example, researchers may use secondary data sources such as published studies or government statistics to investigate relationships between socioeconomic status (SES) and health outcomes that could not be studied in depth using only primary data collection methods such as questionnaires or clinical visits.
Data from primary and secondary sources should be used appropriately when making decisions about healthcare practices.
|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|
The suggested evidence hierarchy provides a framework for ranking studies addressing the numerous characteristics of an intervention at an acceptable level. This technique moves the emphasis away from the RCT and toward the recognition that alternative research designs may be necessary for different therapeutic concerns. The hierarchy also suggests ways in addition to or instead of randomized controlled trials.