| Type of Basis
Types of basis are ranked in five levels.
"TYPE C basis"
(General consensus)
There is a widespread consolidated consensus. Randomised trials have not been carried out or have been inadequate, but the issue is settled without major controversy: currently, no (further) experimental evidence is felt to be needed.
"TYPE 1 evidence"
(Randomised trial(s) available, strong evidence)
Consistent results have been provided by more than one randomised trials, and/or a reliable meta-analysis was performed. In some instances, one randomised trial can be considered sufficient to support this type of evidence.
Further confirmatory trials do not seem necessary.
"TYPE 2 evidence"
(Randomised trial(s) available, weak evidence)
One or more randomised trials have been completed, but the evidence they provide is not considered definitive (their results are not consistent, and/or they are methodologically unsatisfactory, etc.).
Some controlled evidence has therefore been provided, but confirmatory trials would be desirable.
"TYPE 3 evidence"
(External controlled comparisons available)
Evidence is available from non-randomised studies, with external controls allowing comparisons. Some uncontrolled evidence has therefore been provided, but trials would be desirable.
"TYPE R basis"
(Rational inference)
Little or no direct evidence from clinical studies is available. Yet clinical conclusions can be rationally inferred from available data and knowledge (e.g. by rationally combining pieces of information from published studies and observations; for a rare neoplasm, or presentation, through analogy with a related, more common tumour, or presentation; etc.).
The inference can be more or less strong, and trials may, or may not, be desirable (although sometimes unfeasible).
The background was detailed in:
Casali P, Licitra L, Tondini C, de Braud F, Bruzzi P, Costa A, Cavalli F. START:
a European state-of-the-art on-line instrument for clinical oncologists. Ann Oncol. 1999 Jul;10(7):769-73.
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