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Susceptibility or vulnerability is a construct that refers to characteristics of an individual that are likely to predict an increased risk of developing a disorder, either psychological or physical. However as Ingram et al 1998[1] point out adequate definitions have been difficult to formulate.

Susceptibility may be considered as an element in the etiology or causal account of disorders. While external stress, for example, may occur not all people will react in the same way. So those who succumb to depression following a death of a close relative, are hypothesized to have vulnerabilities that make them more likely to develop the disorder than more resilient others.

Ingram & Price (2010)[2] characterize vulnerability with reference to three features: 1. Vulnerability as a stable trait 2. Vulnerability as endogenous and latent 3. Vulnerabilities relationship to stress.

Psychological vulnerability

Physical vilnerability

Sociological vulnerability

A sub-category of vulnerability research is social vulnerability, where increasingly researchers are addressing some of the problems of complex human interactions, vulnerability of specific groups of people, and shocks like natural hazards, climate change, and other kinds of disruptions. The importance of the issue is indicated by the establishment of endowed chairs at university departments to examine social vulnerability.

Common application: In relation to hazards and disasters, vulnerability is a concept that links the relationship that people have with their environment to social forces and institutions and the cultural values that sustain and contest them. “The concept of vulnerability expresses the multidimensionality of disasters by focusing attention on the totality of relationships in a given social situation which constitute a condition that, in combination with environmental forces, produces a disaster” (Bankoff et al. 2004: 11).

It's also the extent to which changes could harm a system.

Emerging research: Vulnerability research covers a complex, multidisciplinary field including development and poverty studies, public health, climate studies, security studies, engineering, geography, political ecology, and disaster and risk management. This research is of particular importance and interest for organizations trying to reduce vulnerability--especially as related to poverty and other Millennium Development Goals. Many institutions are conducting interdisciplinary research on vulnerability. A forum of that brings many of the current researchers on vulnerability together is the Expert Working Group (EWG).1 Researchers are currently working to refine definitions of “vulnerability”, measurement and assessment methods, and effective communication of research to decision makers (Birkmann et al. 2006).

General principals

Major research questions: Within the body of literature related to vulnerability, major research streams include questions of methodology, such as: measuring and assessing vulnerability, including finding appropriate indicators for various aspects of vulnerability, up- and downscaling methods, and participatory methods (Villagran 2006).


In epidemiology a susceptible individual (sometimes known simply as a susceptible) is a member of a population who is at risk of developing a disorder, if he or she is exposed to precipitating causes

Mathematical model of susceptibility

The proportion of the population who are susceptible to a particular disease is denoted S. Due to the problems mentioned above, it is difficult to know this parameter for a given population. However, in a population with a rectangular population distribution (such as that of a developed country), it may be estimated by:

Where A is the average age at which the disease is contracted and L is the average life expectancy of the population. To understand the rationale behind this relation, think of A as the length of time spent in the susceptible group (assuming an individual is susceptible before contracting the disease and immune afterwards) and L as the total length of time spent in the population. It thus follows that the proportion of time spent as a susceptible is A/L and, in a population with a rectangular distribution, the proportion of an individual's life spent in one group is representative of the proportion of the population in that group.

The advantage of estimating S in this way is that both the average age of infection and average life expectancy will be well documented, and thus the other parameters needed to calculate S will be easily at hand.

The parameter S is important in the mathematical modelling of epidemics.

See also


  1. Ingram, R. E., Miranda, J., &C Segal, Z. V. (l998). Cognitive Vulnerability to Depresion. New York: Guilford Press
  2. Ingram, R.E. & Price, J.M. (eds.)(2010) Vulnerability to Psychopathology. New York:Guildford
  • Bankoff, Greg, George Frerks and Dorothea Hilhorst. 2004. Mapping Vulnerability. Sterling: Earthscan.
  • Birkmann, Joern (editor). 2006. Measuring Vulnerability to Natural Hazards – Towards Disaster Resilient Societies. UNU Press.
  • Thywissen, Katharina. 2006. “Components of Risk: A comparative glossary." SOURCE No. 2/2006. Bonn, Germany.
  • Villagran, Juan Carlos. "“Vulnerability: A conceptual and methodological review." SOURCE. No. 2/2006. 4:44, 5 October 2006. Bonn, Germany.