There are six types of evidences accepted in the literature

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Pratyaksha: What is seen or observed directly. These are observational studies and accepted in the scientific community.
Anumana or the evidence based on the inference of a defined hypothesis
Upamana are the evidences based on analogies
Arthapathi are the evidences, which are based on circumstantial evidence
Anupalabdhi is an evidence based on the theory of negation
Shabda is undisputed evidence as it is written in text books and taught to us
Let us take an example to further understand this.

Here is a statement “Neem or Azadirachta indica is a good antiseptic.”

Pratakysha: I would look for any observational study.
Anumana: I will look for any double-blind study in the literature
Upamana: As per Ayurveda, any plant which is bitter in nature will have anti-pitta qualities
Arthapati: Circumstantial evidence and
Anupalabdhi is evidence by negation.
Shabda: Would refer to Sushrut Samhita reference as gold standard.
An Ayurveda doctor will follow the Shabda evidence, but a modern medicine doctor would prefer Anumana as evidence. But both are accepted evidences.


Original (primary) researchis based on data collected from individuals or clusters of individuals, with clusters defined by physician, clinic, geographic region, or other factors.
Within primary research, the hierarchy of evidence must be considered to minimize the risk of bias.
For studies evaluating therapy or harm, well-conducted randomized clinical trials are superior to observational studies, which are superior to unsystematic clinical observations
Questions regarding benefits (and harms) of an intervention are best answered with randomized controlled trials; whereas questions regarding risk factors for disease and prognosis are best answered with prospective cohort studies.
Systematic reviews and meta-analysesare best for answering single questions (e.g. the effectiveness of tight glucose control on microvascular complications of diabetes). They are more scientifically structured than traditional reviews, more open about how the authors attempted to find all relevant articles, judge the scientific quality of each study and weigh evidence from multiple studies with conflicting results. Systematic reviews pay particular attention to including all strong research, whether or not it has been published, to avoid publication bias (positive studies are preferentially published).
Summaries and guidelinesrepresent the highest level of complexity. Ideally, guidelines are a synthesis of systematic reviews, original research, clinical expertise, and patient preferences. At their best, summaries and guidelines are a comprehensive synthesis of the best available evidence, from which the guidelines themselves follow. Guidelines should therefore be based on a critical appraisal of the relevant original research and systematic reviews. There are several examples of multiple guidelines on the same topic making contradictory recommendations
The accepted standards for guideline development include:

Rely on systematic reviews
Grade the quality of available evidence
Grade the strength of recommendations
Make an explicit connection between evidence and recommendations
Strength of the recommendation: A recommendation is a strong recommendation to do (or not do) something, where the benefits clearly outweigh the risks (or vice versa) for nearly all patients.

Grade 1 reflects a strong recommendation. A weak recommendation is made either when risks and benefits are more closely balanced or are more uncertain. Grade 2 reflects a weak recommendation.

Quality of evidence

Assessment of evidence quality in GRADE reflects confidence in the estimates of benefits, harms, and burdens.

GRADE can be implemented with either four levels of evidence quality or with three levels such that the “low” and “very low” categories are combined. The three levels use a letter (A, B, or C) for high-, moderate-, or low-/very low-quality evidence.

High-quality evidence typically comes from well-performed randomized controlled trials or other overwhelming evidence (such as well-executed observational studies with very large effects).
Moderate-quality evidence typically comes from randomized trials with important limitations or from other study designs with special strength.
Low-quality evidence typically comes from observational studies or from controlled trials with very serious limitations. Very low-quality evidence typically comes from non-systematic observations, biologic reasoning, or observational studies with serious limitations.
Based on the above we must come out with strength of evidence and quality of evidence for every Ayurveda treatment.

Let us review Azadirachta indica in Pubmed

There are 2467 studies on the subject.
There are over 138 mentions in headings.
There are 92 RCTs.
There are 308 systemic reviews
There are 30 observational studies
The conclusion that can be drawn is that from modern medicine point of view, Azadirachta indica will have Grade 1A scientific evidence that it has medicinal properties.

Dr KK Aggarwal

Padma Shri Awardee

President Elect Confederation of Medical Associations in Asia and Oceania (CMAAO)

Group Editor-in-Chief IJCP Publications

President Heart Care Foundation of India

Past National President IMA