A vulnerability index is a composite of indices, also referred to as integrated indices, which are quantitative indicators similar to scales, which, when entered into a formula, deliver a single numerical result which can be used for triage (prioritization) and policy analysis. Through their use, ““diverse issues can be combined into a standardised framework…making comparisons possible”. For instance, variable from physical science can be combined with social, medical and even psychological variables to evaluate potential complications in disaster planning contexts. The development of vulnerability indexes as a policy planning tool occurred at the instance of the United Nations Environmental Program and one of the participants in the early task forces has also conducted secondary research documenting the evolution of the analytic tool through various stages.  The term and methodology then proceeded to promulgate  through medical literature and social work as discussed by Dr. James O'Connell of the Boston Healthcare for the Homeless.
The basic methodology of constructing a vulnerability index is described by Briguglio and is quite simple and not without antecedents. Different relative importance is assigned to the different factors (weighting). A cumulative score is then generated. Through application of variable scenarios decision trees can be developed reflecting alternative policy options.Much of the original research has been evaluated by Lino Briguglio and presenters at Oxford, providing a body of secondary source material which is known primarily to workers in specialized areas of development.
A modern concept of a composite vulnerability index grew out of the work of South Pacific Applied Geoscience Commission (SOPAC), Fiji, and the Expert Group on Vulnerability Index  affiliated with the United Nations.
“in response to a call made in the Barbados Plan of Action, the Alliance of Small Island States (AOSIS)”
A prominent observer and participant in development of the vulnerability index model is University of Malta researcher Briguglio for international organizations of small island developing states.  UM also hosts the Islands and Small States Institute, Foundation for International Studies,. Other institutional participants included the New Zealand Official Development Assistance (NZODA) Programme  In 1996, the concept of a composite vulnerability index had been taken up by policy analysts in the Commonwealth but still on only a tentative basis.  In 1997, official background papers of the SIDS unit reflected the term “vulnerability index” at least internally. It was also advanced in Commonwealth channels. By 1997, the term was approved for publication by the staff of the Secretary-General of the United Nations in the SG’s Report on Development of a Vulnerability Index for SIDS.  This concept was subsequently adopted by other experts in that field. and explicitly named as such. 
In a 1999 Technical Report for SOPAC, Kaly et al discussed more specially designated vulnerability indexes. A subsection of that report was entitled “. Vulnerability index – environment” and the report also discussed a newly minted concept of “Environmental vulnerability index”.
Extension of the general concept
The IPCC embraced vulnerability as a key category in 2001.  A 2002 paper then applied a vulnerability indexing model to analysis of vulnerability to sea level rise for a US coastal community. At a 2008 Capacity Building Seminar at Oxford, the “Climate Vulnerability Index” had been fully developed and was  presented with an application to the protection of tourist economies, which may be important to small island states and others. By the time of this seminar, vulnerability indexes were established as tools of governance .
A “Histopathological Plaque Vulnerability Index (HPVI) “ was proposed in a 2005 paper by Tang, et al, entitled Local Maximal Stress Hypothesis and Computational Plaque Vulnerability Index for Atherosclerotic Plaque Assessment. Thereafter, the term was adopted by Dr Jim O’Connell , who is author of a textbook on healthcare in shelters. From his post at Boston’s Healthcare for the Homeless, the model was adopted by Common Ground, an advocacy organization in New York City which has promulgated its organizing model using the vulnerability index to, Santa Monica, New Orleans, Washington, DC, and what their literature refers to as “Los Angeles County’s infamous Skid Row”. It utilizes only eight key key health indicators puts a chronically homeless person at significant risk of dying. The model is now being adapted to and utilized in Australia , with the on-site support Common Ground personnel and has been used in registry week drives in the “ inner city areas” of Brisbane, Melbourne and Sydney.