Rethinking Human Security

1. Introduction: Rethinking Human Security (Pierre Sane). 2. Human Security and Human Rights Interaction (Wolfgang Benedek). 3. Conceptualising the Environmental Dimension of Human Security in the UN (Hans Gunter Brauch). 4. The Ethical Challenges of Human Security in the Age of Globalisation (J. Peter Burgess). 5. Building the Agenda of Human Security: Policy and Practice within the Human Security Network (Keith Krause). 6. Gender Aspects of Human Security (Ghada Moussa). 7. Basic Elements of a Policy Framework for Human Security (Paul Oquist). 8. The Uncertain Future of Human Security in the UN (Taylor Owen). References. Index.

Although YIHS is most useful for developing the population measures of human security described in the next section, we also define a measure that may be more intuitive for some purpose at the individual level of analysis. Thus, Individual Human Security (IHS) is the proportion of the lifespan that a person could reasonably aspire to that he or she can expect to spend outside the state of generalized poverty. This measure, which ranges from zero to one, controls for differences in age. YIHS and IHS are objective measures and so may diverge from an individual's perceived human security. While enhancing per-' ceived human security is an important goal in its own right, the focus of our concern is on objective levels of individual and population human security.
We have formalized these measures of human security QS including discount rates so that risks of entering into a state of generalized poverty in the distant future may be weighed as less important than risks in the near future. Discounting future well-being, or in the present case the risks of being impoverished, has long been debated.41 While it is our general view that future risks should be considered as important or nearly as important as more proximal risks of poverty, the formulation allows for any plausible discount rate. Current practice in a number of fields, such as cost-effectiveness analysis of health interventions, has slowly gravitated to using low positive discount rates of 3 percent or less per year.42 Obviously, once the hard work is done to collect the necessary measures, alternative discounting schemes could also be computed for comparison.

Population Human Security
For the purposes of informing debates on development and security policy, we also provide a definition of population years of human security based on two ways of aggregating YIHS. The simplest measure is the average of YIHS for everyone in the relevant population. If YIHS is 25 for half the people and 35 for the other half, then population human security would be 30. For many uses, this direct average is the most appropriate measure. However, it is sensitive to differences in the population age distribution. If one population is older on average than another, ceteris paribus, it will have a lower population human security. In a strict sense, this is correct. The older population has an expectation of living fewer years above the generalized poverty threshold. But for some comparative purposes, we might like a measure that is unaffected by the age distribution of the population. For such comparative use, we propose to compare groups on the basis of population years of human security at birth.43 The average value of YIHS for newborns today, just like period life expectancy (which is life expectancy at birth), is not affected by the age structure of the population and to a considerable extent reflects a broad range of future risks of survival and generalized poverty in the future.
Both population years of human security and population years of human security at birth are measured on the same intuitive scale as the familiar measures of life expectancy and life expectancy at birth, respectively. They measure the average number of years members of a given population can expect to live (starting from either observed ages or at birth) outside of the state of generalized poverty.
Both concepts exclude future generations in their calculation and thus avoid the standard paradoxes that would otherwise result. For example, without discounting, including future births means that population human security will be the same for almost all populations far enough into the future. Although challenging examples can be found (such as forecast epidemics of infant diseases), we believe that defining population human security as a function of currently living individuals is a reasonable and practical approach. Given the state of the methods of risk assessments, plausible measures of population human security at birth would need to reflect known risks over the succeeding century. This is already a wide window of evaluation, and extending it further into the future is likely to be empirically impractical.
We also exclude from our population measure anything that affects the security of institutions, governments, or other organizations, unless it also affects individuals. This conception of population human security is thus a natural evolution of the literature since Richard Ullman wrote of focusing security on individuals rather than states.44 To measure human security in practice, a set of domains of well-being must be selected. For each domain, a practical indicator must be constructed, as well as the threshold value below which an individual will be defined to be in a state of generalized poverty. Two standard approaches to measuring well-beingmoney-metric utility and the human development index-are instructive examples for this purpose. 43 Another option for an age distribution-independent definition of population human security is to use a standard age distribution to calculate age-standardized population human security (See 0. B. Ahmed et al., "Age Standardization of Rates: A New WHO Standard," GPE discusion paper, no. 31 (Geneva: World Health Organization, 2000). This measure would reflect the complete range of risks of survival and generalized poverty over age and time but has the disadvantage of requiring the selection of a necessarily arbitrary population distribution for age standardization. Some analysts favor using income per capita as a general, all-purpose measurement of well-being, as is amply illustrated by the international focus in policy debates on income per capita. This approach is founded on the notion that each individual can best use the resources they command to maximize their own well-being and that interpersonal comparisons can legitimately be made on the basis of total income. The problems with this approach are well known,45 and when measurement is feasible, most analysts try to include other domains as well. For example, three domains were included in the Human Development Index:46 income per capita, health, and education. Income per capita was not used as an intrinsic domain of well-being but as instrumental for the attainment of many other domains. Health and education were selected because they were considered intrinsic domains of well-being and could be practically measured.
We begin with the Human Development Index domains and so also use income per capita as instrumentally related to several domains of well-being, and also include health and education. Threshold levels of economic well-being and health are clearly important enough to provoke violence. Education per se has not been that important, and so a plausible case might be constructed'that it could be omitted; but people have often fought over the cultural values reflected in education. In addition, we wish to capture contributors to generalized poverty related to other basic freedoms. The UNDP recognized the importance of political freedom and democracy, but could not find generally acceptable measures or weights and so could not include it with their other measured domains. Since we only need a thteshold, and no weights, it will be somewhat easier for us to include variables like these. Thus, our suggestion for a parsimon i~u s set of domains for measuring human security would be income, health, education, political freedom, and democracy. Many other domains of wellbeing come in indirectly through these. In addition, any aspect of well-being that directly affects life expectancy, such as the environment or biodiversity, will to an extent be automatically included in our measure of human security without having to establish a separate domain or threshold.
For each domain explicitly included, we must select an indicator or indicators that reflect our current state of information, as well as the threshold value below which an individual would be in a state of generalized poverty. We now suggest measures of each of these domains, but we emphasize that our framework can easily accommodate any number of additional domains.

Domain-Specific Measures
Although the System of National Accounts (SNA) was developed in the 1950s and has been nearly universally adopted, many variants of income per capita 45 World Bank, World Development Report, 2 0 0 0 4 (New York: Oxford University Press, 2000). 46 UNDP, 1990. could be used.47 Because we emphasize comparing the purchasing power of different individuals across the world, we believe a good measure is GNP per capita converted into international dollars using purchasing power parities.48 The World Bank has proposed that the global definition of absolute (economic) poverty is less than $365 per capita per year in 1985 international dollars49 and this definition has now been widely adopted in the international community (for example, World Bank, DFID). According to this definition, 1.3 billion individuals now live in poverty.50 Like any threshold, this one is arbitrary but has been set at such a low value that no one can credibly argue that individuals with less than $365 per capita are not in generalized poverty. While a good case can be made for raising the poverty threshold, our goal is to codify existing international consensus, and this is the closest (we have at present. Health factors are included in the definition of human security in two distinct ways. First, survival is a critical component of human security. Increasing mortality rates reduce life expectancy and YIHS, ceteris paribus. Fortunately, mortality forecasting is an active area of scholarly research and policy advice.51 Second, individuals who are alive can fall below a threshold of health status that places them in a state of generalized poverty (for example, being paralyzed from the neck down). Considerable progress has been made in the development of comparable measures of the nonfatal dimensions of population health.52 A variety of survey instruments have been developed such as SF-36,53 Euroq01,5~ and WHODAS,55 which can be used to measure various aspects of 47 There are two major choices. First, income per capita can be calculated on the basis of goods and services produced within a country (Gross Domestic Product) or it can be corrected for net property income from abroad (Gross National Product). The distinction is important for countries where remittances or income from investments abroad is substantial. The other key choice is the method of converting incomes per capita in national currency units into a common metric for the purposes of cross-national comparisons. Because official exchange rates do not reflect purchasing power parity for nontraded goods and services such as primary education, an alternative method based on measuring prices and computing purchasing power parities has been developed. See Robert Summers and Alan Heston, "The Penn World  (2): 327-68. Such PPP based comparisons are expressed in "international dollars," which is U.S. dollars in purchasing power terms. 48 The two main estimates of purchasing power parity, based on GDP and GNP per capita, are the Penn World Tables (Summers and Heston 1991) and the World Bank (World Development Indicators 1999), respectively. Unfortunately, the correlation of these two measures is not high enough to make the choice ignorable. 49 World Bank, 1990. World Bank, 1999. 51 World Health Report, 1999and 2000 Murray, Salomon, and Mathers, "A Critical Examination." individuals' health. In parallel, work on how individuals value time spent in different health states provides a basis for an overall assessment of the severity of health states.56 Health states are valued on a scale from 0 (death) to 1 (full health). Severe states such as quadriplegia score around 0.2 and severe depression is 0.6." We would suggest that any individual in a health state less than 0.25 is in a state of generalized poverty.
Most of the rich academic literature measuring democracy and political freedom considers each ~eparately.~~ One of the most commonly used measures is provided by Freedom House, a nonprofit, nonpartisan organization. Freedom House judges democracy by quantifying political rights and political freedom by quantitative measures of civil liberties, which "include the freedoms to develop views, institutions, and personal autonomy apaqt from the state."5g Over 800 other measures of political freedom and democracy have been cons t r~c t e d ,~~ but almost all focus on evaluations of governments rather than the political security of their citizens. This means that to measure the political component of generalized poverty properly, we need additional work. One reasonable threshold for the generalized poverty level for democracy could be the right of an individual to vote in at least one free and fair election (not necessarily national) that affects some important aspect of that person's life. This is quite a minimal level of democracy that the international community would surely want to improve, but without this right a person should clearly be seen as severely deprived. The analogous country-level measure might be the fraction of adults who can participate in such elections. Interestingly, such a measure would likely be greater than 0 percent and less than 100 percent in all but a few countries.
The two main options for measuring educational attainment include literacy and average years of schooling. The advantage of literacy is that it incorporates a qualitatively meaningful threshold of educational attainment in its definition. Most would agree that being illiterate places an individual in a state of generalized poverty. On the practical front, the problem with literacy is that it is notori~usly difficult to compare across countries because self-reported lit- 59The methods of Freedom House can be found at http://www.freedomhouse.org/survey99/ method/.
Kenneth A. Bollen and Pamela Paxton, "102532: Cross-National Indicators of Liberal Democracy, 1950Democracy, -1990." Data set at the Inter-University Consortium for Political and Social Research, Ann Arbor, Michigan (http://urww.icpsr.umich.edu., 1999). eracy differs substantially across countries. Average years of schooling, on the other hand, is a more robust measure of educational attainment.61 An appropriate threshold for average years of schooling might be five or six years, which reflects basic primary education. If a comparable measure of literacy becomes available, we would propose to use it also.

Data Needs
Measuring population human security requires as its starting point good information on the current and past levels of income, health, education, democracy, and political freedom for individuals in different populations of the world. To estimate generalized poverty, however, we need information on individuals within populations simultaneously for these key variables. As the definition of generalized poverty is based on falling below the critical threshold in any of these domains, we require information on the levels of each variable for each individual. In other words, information on health that cannot be related at the individual level to the information on income or political freedom cannot be used alone to estimate generalized poverty for a population.
In practice, we could use available detailed data collections such as national accounts or vital registration to measure the variables separately, and a much smaller study to estimate their joint distribution. As a last resort, methods of ecological inference could be used to infer the joint distributi~n.~~ Scholars have made substantial progress moving from national aggregate data on income to information on the distribution of income.63 We believe that the natural next step, consistent with trends in data collection and with the movement toward human security, is to broaden the collection scheme to cross-domain measures at the individual level. In some cases, adding information on education and proxies of wealth or income to routinely collected health information may be relatively inexpensive. This would be especially valuable since this health information is already collected in relatively standard forms in almost all countries.
Not withstanding this agenda for the future development of generalized poverty information systems, new methods need to be developed and applied to estimate the joint distribution of health, education, income, and political freedom. Fortunately, much can be done. For example, the World Health Organization has a project to use national income and expenditure surveys, along with satellite mapping of the world's population and several geographic factors, to map the location of the world's economically impoverished. Preliminary re-  sults of this project are illustrated in Figure 1, which shows the density of poor individuals per square kilometer for each continent. This mapping of the world's poor amply illustrates the major difference between those in absolute poverty and individuals whether rich or poor who live in the poorest countries. of the world with high densities of poor include Bangladesh, the Ethiopian Highlands, the Ganges Valley, and the Great Lakes region of Africa and Nigeria. Work is underway to use other sources such as demographic and health surveys to estimate the distribution of individuals in different states of health.65 Human security is a forward-looking concept: to measure it today we must project generalized poverty and survival tomorrow. Projections require the development of methods of risk assessment with predictive validity. Such models can best be developed if relatively long historical data bases are available so that the relationship between generalized poverty in each domain, and key social, economic, cultural and political factors, can be explored. Risk assessment is thus a two-stage process. Key factors in accounting for large changes in human security, such as wars, global warming, earthquakes, other natural disasters, and economic crises must be identified prior to projecting generalized poverty itself. In some cases, the areas of health, income, education, and political freedom require as a first step models to assess the risks of these events. Below, we use the challenge of risk assessment of military conflict to illustrate directions for progress in measuring human security.
One important purpose of measuring human security is to provide individuals with better information on their own human security. By so doing, we will tend to increase each individual's perceived human security because humans tend to overestimate threats to their own security. However, measuring human security will also be a critical input to public policy debates on how to enhance population human security. Individual risk assessment models naturally lead to actions to prevent or decrease the prospects of generalized poverty. Measuring human security will also focus the international foreign policy debate on the key contributors to human insecurity and thus improve public policy. To facilitate these goals, we propose that necessary data bases and models be developed that allow for the annual calculation of this human security index. As with all efforts at comparative assessment, annual or periodic reporting of population human security will help all countries understand their situation and inform them about where to make improvements.
Human insecurity can code from any source that increases the risk that people will remain in or enter into a state of generalized poverty. Since gen6ralized poverty is a state that is often difficult to exit, existing in this state is one of the major threats to human security-that is to being in generalized poverty in the future. Others include crime, military conflict (group violence), nonpeaceful transfers of governmental power, diseases and other public health problems, acute environmental disasters (floods, droughts, earthquakes, weather storms, hazards from space, contamination), long-term environmental changes (global warming, ozone hole, water shortage, pollution), and economic crises.
Some components of generalized poverty, such as income, health, and education, have witnessed considerable global progress in the last half-century. For example, the dramatic success of the international community in contributing to the expansion of global life expectancy from 46.5 years in 1950-1955 to 65.4 years in 1995-200066 is an example of the progress that can be made.

Categories of Eflorts to Enhance Human Security
We categorize efforts to enhance human security, ranging from ex ante to ex post, as risk assessment, prevention, protection, and compensation. Risk assessment involves improving and communicating knowledge of the risks that particular populations will enter into or remain in a state of generalized poverty. Prevention includes efforts to reduce these risks. Protection includes those actions that decrease the harm from the events if they occur. Compensation includes efforts to provide financial or in-kind payments to those in generalized poverty. To arrive at these categories, we began with the scheme originally developed by Lincoln Ched7 and then slightly expand it to highlight the importance of risk assessment as distinct from prevention.
This categorization can be used to construct more detailed operational strategies for increasing human security, based on new public policies and academic research. For example, military conflict risk assessment should include research on forecasting military conflict, communicating the risks to those for whom it can make a difference, and developing surveillance systems. Prevention involves estimating causal models of war, identifying modifiable causes, using risk assessments to target conflict reduction interventions, UN Security Council efforts, and national and international deterrence efforts. Protection from military conflict includes trying to change the weaponry of war, such as the campaign to ban landmines and cluster bombs, reinvigorating and extending the international laws that protect noncombatants, and protecting social service delivery and public health systems from combat. Compensation includes war insurance schemes (with risk rated on the basis of existing forecasting models) and various types of humanitarian assistance.

Advantages of Improving Risk Assessment
Even a cursory examination of the major threats to and strategies for enhancing human security highlights risk assessment as the major important and underin-vested area. Risk assessment is critical even for merely measuring population human security, but the advantages of improving risk assessment go far beyond simple measurement.
First, improving methods so that meaningful risk assessment can be undertaken is an important research endeavor in its own right. This type of knowledge in and of itself should be considered a public good. In addition, better knowledge of specific risks might be used by the international community to make more effective public policy. Many efforts at prevention require knowledge of risks; for example, effective response to human security risks is enhanced by early warning systems and hence good risk assessment.
We also know that much psychological and social-psychological research demonstrates that people tend to overestimate risks of the components of generalized poverty.68 By providing high quality risk assessments and disseminating this information to the public, individual perceived human security in many settings can be enhanced. In those settings where individuals underestimate their human insecurity, better risk assessment will allow them to take action at the individual, household, or government level to mitigate against the impact of these risks if they occur.
Third, even if individuals' assessments of their average future well-being are unbiased (that is, correct on average), psychological research indicates that people tend to evaluate the uncertainty in forecasts incorrectly. As such, better risk assessment that is widely and informatively disseminated can increase individual perceived human security directly by reducing forecast variances. Perhaps most obviously, better risk assessments make new interventions possible. For example, accurate hurricane forecasts eliminate most of the immediate public health risk of these severe weather events.
Our approach to using risk assessment in the definition of human security also has the advantage of encompassing other important problems not affecting current human well-being. For example, biodiversity, which is seen by the scientific community as one of the most important global problems, has little or no effect on current well-being. Approaches that provide an agenda for the international community that are not forward-looking would either ignore biodiversity or append it to the agenda in a logically incoherent fashion. Under our approach, even though biodiversity has no effect on current well-being, it is essential in maintaining future well-being and hence plays a central role in improving human security.
Risk assessment is important for forging policies based on the forward looking concept of human security, which can be far more effective than basing policy on current well-being or generalized poverty. Since fighting the last war is obviously not the goal of the international community, we need to prepare responses to what is likely to occur and not merely because prevention is less costly than post-hoc responses. We hope that by illuminating the central role of risk assessment in human security that we are able to point to areas where the academic community can help. Risk assessment is under-researched in some areas and undervalued in others. Most of the social sciences, for example, have an understandable focus on estimating causal effects. What scholars need to understand, however, is that this focus need not come at the expense of models that forecast well. Forecasts are often observable implications of the same models used to estimate causal effects and can also be used to validate those same models. Put in reverse, many causal models now used can be marshaled to improve our forecasts and hence our measurement of human security.
We designed our version of human security to be logically rigorous and to satisfy what appears to be the outline of an emerging normative consensus in the international community. As we go to press, we can report on a commitment from the World kealth Organization to develop and apply new survey tools to measure health and related domains of human security that follow the suggestions in this article. In addition, we note that in a recent speech, Mexican President Vincente Fox has adopted the notion of human security offered here.

Normative Decisions
Our concept is based on the security of human beings, rather than the protection of state boundaries, with each individual contributing equally to population human security. The definition is forward looking: an individual's current security is a function of her or his future prospects. Most distinctively, human security is a function of the risk of being below a threshold of well-being, what we call a state of generalized poverty, rather than average levels of well-being.
Using generalized poverty means that a policy based on human security focuses effort primarily on human beings in the most dire situations. This is a logical extension of what was effectively the perspective of the international community in the domain of health when over the last forty years it generated unprecedented increases in the human life span by first addressing severe childhood illnesses. The alternative view would be to focus on increasing average levels of human well-being (otherwise known as human development). While we do not think human security has any necessary, absolute, or lexicographic priority as a goal of social policy in comparison to human development, most in the international community seems to believe that it should have some priority except in somewhat unusual situations.
Recent academic debates have led to related distinctions. For example, the prioritarian view holds that we should be interested in improving the well-being of everyone with a special concern for the well-being of the worst off.69 This view can be distinguished from the classical egalitarian perspective, which is concerned with the entire distribution of well-being across individuals. Thus, an egalitarian might agree with a public policy that sacrifices a degree of wellbeing among the best off in order to reduce inequality, but in some cases a prioritarian would object.
Any priority for human security over human development should not be considered absolute, and we would not argue against public policy that enhances human development simply because human security had not been maximized first. But we believe that the international development and security communities are primarily focused on enhancing what we call human security. One way of thinking about these normative preferences is to derive them from the deeper goal of maximizing global human utility. From this perspective, the issue is how we make interpersonal utility comparisons. According to our interpretation of the emerging consensus of the international community, a small increase in well-being across the generalized poverty threshold produces a considerably larger change in utility than all but the most extreme changes in human well-being at other levels. If this is true, then the priority of human security over human development is an automatic consequence.

Agenda for Foreign Policy and Scientific Progress
The definition and measure of human security offered in this article are intended to formalize the emerging consensus in the international community over some of its most central goals. Since the idea of human security is to improve the lives of people rather than improve the security of national borders and key issues cross these borders, coordinated action by the international community seems essential. Continued linkages and cooperation among governments, international organizations, nongovernmental organizations, and other parts of civil society will also be important.
If this is a reasonable statement of the emerging consensus, future directions for development and security policies will be greatly affected. We now consider examples of policy and research strategies that would be affected within the four strategies for improving human security-risk assessment, prevention, protection, and compensation.
One of the areas with the largest potential gains is improving risk assessment for the key causes of generalized poverty. Building the capacity in data bases and methods to undertake better risk assessment should be a central component of a human security-focused foreign policy. The potential for improved risk assessment seems substantial in developing surveillance systems for new diseases, for example. Similarly, recent progress in risk assessment methods in political science means that for the first time some military conflicts can be accurately predicted, which may mean that risk assessment for some other key causes of human security can also be rapidly improved. Such efforts could be greatly enhanced by forging new interdisciplinary ties. For example, political scientists have focused almost exclusively on elite political decisions to go to war, rather than war's ultimate public health consequences, and hence on only one aspect of risk assessment and prevention. Public health professionals have not taken advantage of these developments, but have much to contribute in the areas of protection and compensation that political scientists have not engaged?O Better prevention strategies could be built on improved risk assessment. For example, in the area of military conflict, better causal models and risk assessments might provide the opportunity for more focused foreign policy interventions to reduce the risk of conflict. Information given to the public in countries or communities with elevated risks of conflict may in and of itself decrease the risk of conflict. Other strategies for prevention that have been proposed and seem likely to be productive include improved international and national monetary institutions to reduce the risk of economic crises, carbon-trading agreements to reduce green-house gases and the risk of global climate change, and improved rapid response teams to minimize disease transmission in response to reports from surveillance systems.
While we believe, like others, that risk assessment and prevention may be the most rewarding direction for international efforts to enhance human security, there are also substantial opportunities in the area of protection. The recent success in the campaign to ban landmines has opened up the prospect of other international agreements to make the weapons of war more focused on combatants, thus reducing the insecurity of noncombatants. International efforts to develop agreements on cluster bombs have a similar motivation. Other strategies for protection include efforts to enhance the quality of buildings in earthquake-prone areas, as well as social mechanisms to protect vulnerable groups during economic crises. Humanitarian disaster response is also a form of protection.
Finally, the international community could enhance efforts at compensation by creating organizations to provide insurance against the financial costs associated with major risks to human security. Most nations effectively self-insure against the costs of major catastrophes. The end result is that many find themselves facing long-term impacts of crises, whether Hurricane Mitch or civil war. Traditional concepts of insurance could perhaps be developed to provide nations at high risk of these events with some financial risk protection.
More detailed implications for policy would, we believe, follow from a structured application of this framework to the challenges of human security. At this point, building the evidence base for human security must be a priority if the focus of international action is to move from reacting to the latest humanitarian crisis to effectively enhance human security through risk assessment, prevention, protection, and compensation." We define individual human security to be YIHS, = J; [I -P, (t 1 ~)]~~(t)Wdt, where P(t lo) is the probability of individual i being in a state of generalized poverty at time t given a vector of thresholds that define generalized poverty in critical domains of well-being, conditional on being alive, and S(t) is the probability that the individual is alive at time t (the so-called survivorship function). Thus, if an individual has an elevated risk of death in the future, manifested by a decrease in S(t), then their individual human security has decreased. The discount factor is T, which equals one if the prospect of being in a state of generalized poverty in the distant future contributes as much to years of an individual's human insecurity as the prospect of being in generalized poverty in the near future. When A is less than 1 then the prospect of being insecure in the distant future contributes less than in the near future. In addition, P(t) and S(t) are each conditional on the information set available. In the present case, we define the information set as including all data available to at least one person, but not necessarily the person for whom we are calculating YIHS. Individuals who pay a lot of attention, are smart, have sociological imaginations, have access to education and other knowledge, etc. will often be able to do better than a statistical analyst in forecasting, since they condition on more information. Others who are not so fortunate will probably not be able to forecast as well as a statistical analyst. Thus, part of the goal of the international community probably ought to be to equalize the information sets by distributing information about our forecasts.
YIHS is analogous to the familiar period life expectancy measure, a calculation based on mortality rates by age observed for a single period of time, usually a year. Period life expectancy is the average length of life for a hypothetical group of newborns born today who would experience over the course of their life currently observed mortality rates at each age. As such, period life expectancy is a convenient summary measure of current mortality experience, even though it does not pertain to any actual group of individuals. The proposed measure of human security is also based on the concept of a life table with two key modifications. First, human security is by definition about the future and reflects our uncertainty about the future. Individual human security is thus always calculated prospectively. Second, we are applying the concept of life expectancy at the individual level. Period life tables are usually calculated for populations. At the individual level, however, the concept of life expectancy or the area under the individual's survivorship function can be applied prospectively.
To clarify potential differences between YIHS and individual perceived human security (PYIHS), we define the latter formally as, PYIHS, = ];[I -Pf(t(~~)]Sf(t)Gf(t)dt, where T, is the vector of thresholds that individual i uses to define for herself a state of generalized poverty. For example, auto workers in Detroit faced with the prospect of unemployment may perceive themselves as insecure because the threshold they use to define deprivation is much higher than the global income poverty threshold. Sf(t) is the subjective survivorship function for individual i and Pf (t 1 hi) is his or her subjective probability of falling below the generalized poverty threshold. Individuals are well known to overestimate small risks and underestimate large risks,' l so that their subjective assessments underestimate their human security in secure environments and overestimate them in risky environments. They also generally have a different information set available to make forecasts than we use to define YIHS. This formulation of PYIHS also includes individuals' discount rate for the future. PYIHS is based on an individual's forecasts of the probability of being in a state of generalized poverty, as well as on forecasts of survival. This measure of PYIHS is strictly relative to the expectations and subjective probabilities of the individual. In other words, PYIHS could increase (as we all know from real life experience) not because the actual probabilities of generalized poverty or survival have changed but because an individual's subjective assessment of these changes or their discount rate changes.
Because we have chosen to define population human security in terms of forecasted generalized poverty and survivorship does not mean that we think that an individual's own assessments of their human security is unimportant. Clearly, if population human security is high but most individuals perceive that their human security is low, this is a concern for public policy and for the community as a whole. Simply providing the public with better risk assessment may serve to enhance perceived human security if people have overestimated risks of generalized poverty or death. Nevertheless, from the vantage point of development and security, we believe that population human security based on estimated probabilities is of the greatest policy relevance.
IPHS may be based on the high discount rates that many individuals, especially the poor, use in their daily life decisions. We also know that discount rates used for policy decisions, such as investments in water or environmental projects, are typically and reasonably much lower than individual discount rates.72 Based on long-standing arguments against discounting future utilityJ3 we believe that a reasonable approach is to evaluate the risks of generalized poverty five years hence as being as important or nearly as important as in ten years.
Finally, we define where Sf (t) is the standard survivorship function for someone with the sex and age of individual i. The denominator is the discounted expected years of life an individual can reasonably aspire to. In this way, if an individual faces an increased risk of death in the future, IHS will decrease.