Two-way indicator species analysis

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Two-way indicator species analysis (TWINSPAN) is a Fortran-based statistical analysis method described in 1979 by Mark O. Hill. It is widely used in ecological research.{{Cite journal |last1=Vermeerscha, Sophie |last2=de Genstc, William |last3=Vermoesend, Frank |last4=Triestb, Ludwig |year=2003 |title=The influence of transformations of an ordinal scale of a floristic gradient, applied on a TWINSPAN classification |journal=Flora - Morphology, Distribution, Functional Ecology of Plants |volume=198 |issue=5 |pages=389–403 |doi=10.1078/0367-2530-00111}}

As of 1997, it was the only widespread standardized method to identify indicator plants.{{Cite journal |last1=Dufrene |first1=Marc |last2=Legendre |first2=Pierre |date=August 1997 |title=Species Assemblages and Indicator Species: The Need for a Flexible Asymmetrical Approach |url=http://www.jstor.org/stable/2963459 |journal=Ecological Monographs |volume=67 |issue=3 |pages=345 |doi=10.2307/2963459|jstor=2963459 |hdl=2268/145383 |hdl-access=free }}