Developing indicators for environment and health John T. Wiflsa & David J. Briggsb
The need for information Reliable, valid, up-to-date information and statistics are essential for supporting policy, monitoring the effectiveness of management, directing research and informing the general public (1). This was confirmed by the Rio de Janiero Earth Summit in 1992: "The need for information arises at all levels, from that of senior decision-makers at the national and international levels to the grass-roots and individual levels" (2). This need for information is especially acute in assessing the relationship between the environment and health; the environment affects health in numerous ways, with both beneficial and detrimental effects. The environmentally-related aspects of health can therefore be protected through the inclusion of health considerations in environmental policies. To date, however, health considerations have been very poorly represented in environmental policy. For example, the fifth European Community environmental action programme, launched in 1992, concentrated on target sectors (e.g., industry, energy, and transport) and themes (e.g., waste management and the urban environment). While health was given some consideration, priority was given to general environmental issues. The same is also true of many national environmental policies; for example in the United Kingdom (3) and Italy (4). Conversely, several recent international policy developments encourage the integration of environmental and health concerns. Principle 1 of the Rio Declaration on Environment and Development, for example, states that "Human beings are at the centre of concerns for sustainable development. They are entitled to a healthy and productive life in harmony with nature" (2). In addition, the World Health Organization (WHO) Global Strategy for Environment and Health identifies three key objectives for environment and health; • • • achieving a sustainable basis for Health For All· providing an environment that promote~ health; and making all individuals and organisations aware of their responsibility for health and its environmental basis.
Decision-makers at the international, national and local levels therefore need information at the appropriate scale to monitor and survey the current environment and health situation and to evaluate progress towards achieving policy targets.
Indicators Indicators are one means of providing policymakers with information; representing the end product of a lengthy information chain. Measurements produce raw data; the combination and publication of data produces statistics; statistics are translated and applied, creating indicators. Indicators have an added significance as compared to the underlying statistics and are tied to a specific purpose (5). The word indicator is derived from the Latin verb indicare, meaning to point out, indicate or announce. The use of indicators is well-established in many fields; for example, in the areas of poverty, deprivation and social policy (6, 7), ecology and nature conservation (8, 9), and in economics. Gross Domestic Product (GDP), has long been used as the primary measure for determining wealth and economic development nationally and internationally (10). Other economic indicators include the Retail Price Index (RPI), the Gross National Product (GNP) and the unemployment rate. Social indicators include direct measures, such as educational expenditure per student or the percentage of households living below the poverty line (11, 12) and indirect measures, such as composite deprivation indices (7). In all of these areas, indicators provide an important contribution to policy formulation and the decision-making process. They can be used to fulfil many functions, including; promoting specific policy issues, providing objective baseline information, demonstrating spatial and temporal variations and monitoring the effectiveness of policy actions (1). The development of environmental indicators is currently ongoing at local, national and international levels, with the involvement of many governIJ_lental, non-governmental and international agenCies - from individual community groups concerned about their local environment to international agencies responsible for evaluating national environmental performance. The Organisation for Economic Cooperation and Development (OECD), for example, was given a mandate by the G-7 Economic Summit in Paris, 1989 to "examine 155
Res.earc~er, Institute of Environmental and Policy Analysis, Umverslty of Huddersfield, Huddersfield, United Kingdom. b Professor and Director, Institute of Environmental and Policy ~alysis, University of Huddersfield, Huddersfield, United Kingdom.
•
Wid hlth statist. quart., 48 (1995)
how selected environmental indicators could be developed" (13). The OECD has chosen to adopt the "Pressure-State-Response" framework, based on the premise that "human activities exert pressures on the environment and change its quality and the quantity of natural resources (state). Society responds to these changes through environmental, general economic and sectoral policies (response)" (14). Individual indicators have been developed to reflect environmental pressures, the state of the environment and societal responses. A number of indicator selection criteria have also been identified which embody the main requirements for ensuring indicator effectiveness. In each of 3 main categories, indicators should:
Policy relevance and utility for users - provide a representative picture of environmental conditions, pressures on the environment and society's responses; - be simple, easy to interpret and show trends over time; - be responsive to changes in the environment and related human activities; - provide a basis for international comparisons; be national in scope or applicable to regional issues of national significance; have a target or threshold against which it can be measured; Analytical soundness be theoretically well-founded in technical and scientific terms; be based on international standards and consensus about its validity; - be capable oflinkage with information systems, economic models and forecasting; Measurability be based on data which are available, or readily available at an acceptable cost/benefit ratio; be based on adequately documented data of a known quality; and be based on data which are reliably updated at regular intervals (14). It should, however, be recognized that these criteria represent the ideal for indicator selection; in reality, it is unlikely that indicators can be found which satisfy all of the criteria, particularly in the short-term. In addition, these criteria reflect to a large degree the purpose for which the OECD indicators are intended; namely, to highlight national environmental issues and evaluate national environmental performance. Indicators developed for alternative purposes will therefore require different selection criteria. At the national level, indicator projects are underway in Canada and the Netherlands. In the Netherlands, Environmental Policy Performance Indicators are being developed to reflect the issues identified by the National Environment Policy Plan 156
(NEPP) in 1989 and the NEPP-Plus in 1990 (15). Theme indicators (e.g., ozone depletion and eutrophication) reflect key issues and target group indicators relate to sectors of socio-economic activity (e.g., agriculture and industry). Targets outlined in the policy plans accompany the relevant indicators to illustrate trends and demonstrate the effectiveness of environmental policy. To provide decision-makers and the general public with clear, concise and unambiguous information, the indicators are presented in a highly aggregated format. For example, the indicator for "eutrophication of the environment" comprises combined annual emissions of phosphorus (P) and nitrogen (N) with a weighting factor of 1 for phosphorus and 0.1 for nitrogen (16). Canada is in the process of developing indicators which provide a comprehensive picture of the state of the environment and indicate trends towards the environmental goals of sustainable development. A preliminary set of indicators divided predominantly by environmental media, was published in 1991, with individual indicators reflecting environmental stresses and the state of the environment for particular policy issues (e.g., climate change, ozone depletion and freshwater quality) (17). Since 1992, a series of indicator bulletins have been published which present key indicators for particular environmental issues and illustrate the complexities and cyclical nature of environmental systems. For example, the indicator bulletin for stratospheric ozone depletion describes the environmental route of ozone-depleting substances and presents data for three indicators: "domestic supply of ozone-depleting substances"; "global atmospheric concentrations ofCFC-11 and CFC-12"; and "stratospheric ozone levels over Canada" (18). The concept of environmental indicators has similarly been widely adopted and applied at the local level. Examples include the Jacksonville "Quality-of-Life Project", Jacksonville, Florida, United States of America (11); the Local Government Management Board (LGMB) "Sustainability Indicators Project" in the United Kingdom (19); and the "Sustainable Seattle Indicators of a Sustainable Community" project, Seattle, Washington, United States (20). These projects are based on local sustainable development issues and attempts to assess quality of life, individual indicators being divided by issue rather than by environmental media. While not being based solely on environmental issues, they do include several environmental indicators. For example, indicators used in the Jacksonville project include "river compliance with dissolved oxygen standards" and "tons of solid waste per capita" (11), while indicators used in the Sustainable Seattle project include the "number of days per year air quality fails to meet air quality standards" and "wild salmon runs through local streams" (20). Rapp. trimest. statist. sanit. mond., 48 (1995)
Chart 1 The exposure chain and the relationship between exposure (stress) and health outcome
STRESS Sectors Industry Transport r--
Relation to health outcome Indirect
Ease of collection/ compilation Simple
Level of control Controllable
I
I
Energy Agriculture Waste
I
I
I
Households
I
p
I r---+ I R 0 N M E N T A L D
I
I
I Source activity
I
I
Natural environment I
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I i c y p r i 0
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E N
\~1
Discharge/Emission 1 Environmental
r ·i t y
r-
• •
Ambient concentration
a r 1-e a s .____
0 M A I N
I
Routes of exposure J Human exposure
••• •
"
+
media I
\
+ + +
,, More direct
, Complex
,, Uncontrollable WH095356
H E A L T H
D 0 M A I N
Individual dose Health outcome
~
OUTCOME Indicators for environment and health While considerable progress has been made in the development of environmental indicators, the use of indicators to demonstrate relationships between environment and health is much less well developed. The question of what constitutes an effective environment-health indicator can therefore be posed. In attempting to answer this question, a useful starting point is the principle that environmental impacts on human health operate primarily through physical exposure to various pollutants (though also through exposure to other environmental hazards and less tangible psychological exposures from living and working environments). The link between environment and health is thus provided by the process of exposure. Exposure itself, however, is the product of a relatively long causal chain. As Adriaanse (16) has stated: "... sources or actors cause emissions to the environment, leading to certain concentrations in the living environment via dilution, dispersion and conversion reactions. Receptors (man, flora, fauna) are exposed to these concentrations, with harmful effects". The conceptual model in Chart 1 illustrates the exposure chain in more detail and Wid hlth statist. quart., 48 (1995)
describes the relationship between exposure (stress) and health outcome (outcome). While the majority of these exposures result from human activity, it must be recognized that some are attributable to "natural", or background sources; such as the emission of the carcinogenic gas radon from particular geological formations. Based on the above model, two categories of indicators can be defined; • Health-related environmental indicators (HREI's): definable environmental conditions or trends which suggest potential health effects; and • Environment-related health indicators (ERHI's) health outcomes which suggest an environmental caul)e, or a contribution from environmental factors. The remainder of this article is devoted to health-related environmental indicators.
Developing health-related environmental indicators (HREI's) Based on the above model, the ideal HREI may seem to be exposure. Exposure, being the last link in the environmental chain, is most closely related to individual dose and health outcome. While the 157
connection between some exposures and health effects is epidemiologically well-established, the links are rarely unitary or straightforward (21); different individuals experiencing similar exposures may exhibit a wide variety of health outcomes due to numerous factors, including variations in individual susceptibility, medium of exposure and age. In addition, different social and environmental conditions may act in concert to affect health, while single factors may contribute to a wide variety of possibly contradictory health outcomes. Healthrelated environmental indicators are therefore, by necessity limited to calculating exposure and cannot be used accurately to predict health outcome. To ensure their effectiveness, HREI's should also meet certain selection criteria, although it should be noted that these represent the ideal situation and their relative importance has yet to be evaluated. Inter alia, indicators should: &levance
day- at home, en route to work and at work. While this information can be obtained by personal monitoring, it is both difficult and costly to obtain. The following "proxy" indicators for exposure could therefore be used: source activity: number of vehicles emissions: number, type and speed of vehicles (predicted amount of N0 2) concentration: amount of N0 2 present at monitoring sites (actual amount ofN0 2). Proxy indicators, however, must also comply with the selection criteria identified above. Three factors are of specific importance. 1. Firstly, selection of suitable proxies depends upon the existence of strong relationships between the proxy and exposure. In reality, however, these relationships are often weak and are diminished by the complexity of the processes involved: by the effects of confounding, and by poor data quality. The further removed from exposure the proxy is, the weaker it is likely to be as a reliable indicator of exposure and hence of health effect. Total exposure, for example, is a product of many different exposure events at different times and different locations. Simple measures of pollution levels (e.g., average annual concentration) at a broad geographic scale, or at monitoring stations far removed from the area of concern, are unlikely to provide a reliable indication of exposure. Indicators from yet further up the exposure chain, such as emission levels or industrial activity, are likely to be weaker still. To assess the reliability of a proxy indicator, it is therefore necessary to test the strength of its correlation with the relevant environmental exposure. 2. On the other hand, indicators from earlier in the exposure sequence reflect processes which can be more readily controlled by policy. While little can be done to reduce pollution levels once they have been emitted and dispersed in the environment, relatively rigorous control is feasible at source; for example by regulating emission levels or particular industrial processes. As a result, indicators earlier in the causal chain tend to be more immediately relevant to policy. 3. At the same time, data are more readily available for indicators higher in the exposure chain. As has been noted, direct measurements of exposure are rare. Data on pollution levels in different environmental media are more abundant, but still limited in geographic scope, range of pollutants and quality (1). Data on emissions are also widely available. Many countries now maintain national emissions inventories, while a number of international inventories also exist or are under development (25). Relatively few emissions inventories, however, provide a complete picture of emissions via all pathways and from all sources: the Rapp. trimest. statist. sanit. mond., 48 (1995)
• • •
be based on environmental conditions which are amenable to change; be based on epidemiological relationships between environment and health; be based on definable health-related environmental issues;
Objectivity
• • • •
be reliable, consistent and objective; be sensitive or responsive to changes in environmental conditions; be scientifically valid, i.e., indicate what they purport to indicate; provide a representative picture of healthrelated environmental exposure;
Data
• • •
show trends over time through the use of retrospective data; be based on data which is available at an acceptable cost/benefit ratio; and be based on adequately documented data of a known quality.
The principal problem with using exposure as an HREI is the lack of available data. Measures of exposure are extremely difficult to obtain and are only available for a small number of substances in a limited number of geographic areas; for example, where individual exposure to dioxins has been monitored as part of an epidemiological study to evaluate the relationship between dioxins and congenital malformations (22-24). It therefore becomes necessary to infer exposure by indirect methods -for example, from data on industrial activity in certain sectors, from emissions and from levels of pollution in the ambient environment. For example, for the issue of nitrogen dioxide pollution, the ideal exposure indicator is the amount ofN02 that an individual is exposed to during the 158
Box 1 Indicator survey Indicator source Title Number proposed Number in use Data available
Canada: Environment Canada Canada: Environment Canada Costa Rica: Approximated Sustainability Index Dirgha Tiwari: Asian Institute of Technology EUROSTAT Netherlands: Environmental Policy Performance Indicators Nigeria: Odemerho & Chokor Norway: Environment Ministry OECD OECD United Kingdom: Environment Challenge United Kingdom: Hope/Parker Pilot Environment Index United Kingdom: J. Catford, Wessex Regional Health Authority United Kingdom: Lancaster County Council United Kingdom: Leeds Quantifiable City United Kingdom: Local Government Management Board United Kingdom: Townsend deprivation index United Kingdom: United Nations Association United Kingdom: V. Anderson: Alternative Economic Indicators United Kingdom: WWF/NEF Indicators Initiative United States: Jacksonville Quality of Life Project United States: Sustainable Seattle 1993 United States: World Resources Institute Wid hlth statist. quart., 48 (1995)
National indicators project: preliminary indicators 1991 National indicators project: indicator bulletins 1992-94 Edgar E. Gutierrez-Espeleta: problem, issue and sustainability indicators 1994 Country and project indicators Eurostat pressure index project: illustrative indicators 1994 Theme and target group indicators 1993 Aggregate index of environmental quality 1991 Norway environmental quality indicators project 1992 Preliminary environment indicators 1991 Environmental performance review indicators 1993 Green Gauge: indicators for the United Kingdom environment 1994 A pilot environmental index for the United Kingdom 1991 Proposed positive indicators 1983 98 46 26 37 28 55
43 16
Yes Yes
38 50 14 68 Yes
25
Yes
10 9
Yes
Health-related indicators for a sustainable community project 1994 Leeds quantifiable city project proposed input, output & process indicators 1994 Local sustainability indicators project 1994 Index of social deprivation Measuring sustainability: potential core indicators Suggested priority environmental indicators 1991 Action for indicators: national performance and sectoral indicators 1994 Quality of life indicators 1983-92 Draft indicators of a sustainable community 1993 Proposed environmental indicators for national reporting 1994
198 52
102
83 30 16
75
78 40 26 20
Yes Yes
159
Box 1 (continued) Indicator source Title Number proposed Number in use Data available
WHO: Health For All
WHO Health For All statistical indicators (environmentally-related indicators only) WHO healthy city indicators WHO consultation on developing health and environmental indicators
27
Yes
WHO: Multi-City Action Plan WHO: HEGIS
39 62
1993 Total number of indicators
960
451
233
majority are concerned only with emissions to the air, and many relate only to industrial point sources. The reliability of many emissions estimates is therefore open to doubt, due in part to deficiencies in the input data and the emission models used (25). Data on source activities may also prove unreliable. Identical processes in different locations may produce different emissions over time due, for example, to variations in climatic conditions and raw material quality. Different processes for identical source activities are also likely to produce different emissions.
The utility of existing indicators With the large number of environmental indicators currently under development, there is a need to examine their utility for assessing environmental and health relationships; namely, whether they fulfil the criteria for health-related environmental indicators and if so, what data is available. A survey of 26 international, national, regional and local indicator projects from around the world yielded a total of over 1 400 indicators. As Box 1 illustrates, the majority of these are at the proposal stage, while relatively few are actually in use. Out of a total of 1 411 indicators, 960 have been proposed, while 451 are in use. It should be noted, however, that there is considerable duplication of individual indicators between different projects. For example, 21 of the 26 indicator sets included S02 and N0 2 as indicators, although the definition varied between different sets - from emissions, to ambient concentration, to the number of times air quality guidelines are exceeded. Thus the actual number of issues and substances covered by the various projects is smaller than initially apparent from the number of indicators. However, while many indicators may cover the same issues and substances, the use of different definitions and denominators leads to non-comparability between indicators. For the effective use of non-comparable indicators, it is therefore necessary to refer back up the information chain to the original data on which the indicators are based. Of the 451 indicators in use, data were available for only 233. Some indicator projects are in the 160
early stages ofimplementation and data have yet to be collected; for example, the United Kingdom's Local Government Management Board indicators. Other projects, such as Sustainable Seattle in the United States and Environment Challenge in the United Kingdom, have chosen to adopt a limited number of indicators from a larger range of proposed indicators. Finally, details of two indicators sets were obtained from academic papers (Odemerho & Chokor's index in Nigeria (26) and the Hope/Parker index in the United Kingdom (27)) where insufficient supporting data were given. The 233 indicators (relating to 8 projects), for which data were available, are analysed in Box 2. The indicators were initially assessed for their health relevance; namely, whether they relate specifically to environmental and health problems. Predictably, it was found that indicators developed for primarily environmental purposes (e.g., the OECD indicators), or as quality of life measures (e.g., the Jacksonville indicators), corresponded only partially with environmental and health issues. Next, the indicator coverage and level of data aggregation were examined. Local level data were available for two of the projects (Seattle and Jacksonville) , while national level data were available for the remaining 6; Canada, the Netherlands, the United Kingdom, selected OECD countries and member countries of the World Health Organization's European Region. Data for the indicators were presented for a range of years: 4 of the projects covered the 1970s to 1990s and the remaining 4 covering the 1980s to 1990s. Of the indicators themselves, only 55% were found to correspond to the stress-outcome framework, 45% being in the "other indicators" category. In part, this reflects the intended purpose of the indicator projects. For example, the Jacksonville indicators are intended primarily to provide general information to local decision-makers and members of the public; 91% of the indicators relate to non-environmental issues such as education, the economy, public safety and the social environment, while only 9% relate to the environment Rapp. trimest. statist. sanit. mond., 48 (1995)
iS:: ~
~
Box2 Analysis of 233 indicators already in use
:::;-
s "'
;]i· ,....
§
~~
Indicator sets
Health-related?
Indicator coverage
Level of aggregation
Data period
--.,
~
No. of source activity indicators
No. of emission indicators
No. of concentration indicators
No. of exposure indicators
No. of other indicators
~
<0
Canada: Indicator bulletins Canada: Preliminary indicators Netherlands: Environmental Policy Performance Indicators OECD: Preliminary indicators United Kingdom: Environment ChallengeGreen Gauge indicators United States: Jacksonville quality of life indicators United States: Sustainable Seattle indicators WHO: Health-for-All indicators {environmental only) Totals
Yes Yes
Canada Canada
National National
Mostly 1970s to early 1990s Mostly 1970s to 1990 1980 to 1991 Mostly 1970 to late 1980s Mostly 1980s to 1990s 1983 to 1992
5 (31) 15 (35)
1 (6) 10 {23)
6 {38) 11 (26)
0 0
4 {25) 7 (16)
Yes Partly
Netherlands OECD countries
National International
9 (64) 15 (60)
3 (21) 4 {16)
1 (7) 1 {4)
1 (7) 0
0 5 {20)
Yes
United Kingdom
National
1 {10)
1 {10)
3 (30)
0
5 {50)
Partly
Jacksonville/ Duval County Seattle/ King County WHO/EURO countries
Local
2 {3)
0
5 {6)
0
7t (91)
Partly
Local
Mostly early 1980s to 1990s Mostly 1970 to 1990
5 (25)
0
0
1 (5)
14 {70)
Yes
International
25 (93) 77 {33)
0 19 (8)
2 {7) 29 (12)
0 2 (1)
0 106 {45)
Note: Numbers in brackets denote percentages ol total for ~ach row
~
(13). However, it also suggests that there is a shortage of indicators developed specifically to address environmental and health problems. Among the indicators which do fit the framework, there is a bias towards the earlier categories. Source activity indicators account for 33%, emission indicators for 8%, concentration indicators for 12% and exposure indicators for 1%. While this may stem from the intended use of the various indicator sets it also reflects the shortage of data for indicators in the later categories. As previously mentioned, while data are more readily available for the earlier indicators, they are unlikely to provide a reliable indication of exposure. Considerable doubt therefore remains as to their suitability as health-related environmental indicators. The indicators also fail to meet a number of the identified HREI selection criteria: for example, most of the indicators are based on general environmental issues, rather than specific health-related environmental issues. As Bakkes (7) has noted, "indicators suitable for one function may be totally inappropriate for others". Neither are the existing indicators based on epidemiological relationships: they are therefore unlikely to provide an accurate representation of health-related environmental issues. In addition, the reliability, consistency, sensitivity and objectivity of existing indicators has yet to be assessed. For example, can two researchers using the same traffic-related emissions indicator for N0 2 in two different countries obtain comparable answers, or do the factors involved (e.g., vehicle type and speed) influence the process to such a degree that the reliability and consistency of the results is open to doubt?
Summary This article demonstrates the need for indicators in the policy-making process and presents some of the current work on developing environmental indicators at the international, national and local levels. The paucity of indicators to demonstrate relationships between environment and health is outlined and a causal chain for physical pollutants- from source activity to emission, concentration and exposure- is presented. While indicators can be developed at each of these stages, indicators from earlier in the chain reflect processes which can more readily be controlled by policy; data is also more readily available for these indicators, yet only the later indicators are likely to provide a reliable guide to human exposure. A survey of 26 indicator projects from around the world yielded 8 sets which are in use and for which data exists. These were found to be only partially health-related and heavily weighted towards the source activity indicator category. Their utility as reliable indicators of human exposure is therefore seriously open to doubt and there is consequently a need to develop indicators specifically to assess environmental and health relationships.
Resume Mise au point d'indicateurs environnement et sante Cet article demontre qu'on ne peut elaborer une strategie sans indicateurs et presente certains des travaux entrepris pour mettre au point des indicateurs environnementaux aux niveaux international, national et local. Ayant souligne Ia rarete des indicateurs demontrant un lien entre l'environnement et Ia sante, les auteurs presentent une chaine de causalite pour les polluants physiques: Ia source d'activite- emission- concentration - exposition. On peut certes mettre au point des indicateurs pour chacune de ces etapes, mais ceux qui mesurent les premiers elements de Ia chaine revele des processus plus faciles a maitriser par !'application d'une strategie; les donnees de ces indicateurs sont egalement plus faciles a obtenir, mais seuls les indicateurs portant sur les elements suivants de Ia chaine sont susceptibles de fournir des indications fiables sur !'exposition des individus. Une enquete portant sur 26 indicateurs mis au point a titre experimental dans diverses parties du monde a perm is d'etablir huit categories actuellement en usage et pour lesquelles on dispose de donnees. Ces indicateurs ne se sont ave res que partiellement lies a Ia sante et portent principalement sur Ia source d'activite. Leur utilite en tant qu'indicateurs fiables de !'exposition est done fort discutable, d'ou Ia necessite de mettre au point des indicateurs mesurant tout specialement les liens entre l'environnement et Ia sante.
Conclusions While considerable progress has been made in developing environmental indicators, the use of indicators to demonstrate relationships between environment and health is clearly less well developed. From the analysis above, it is clear that the majority of existing environmental indicators are unsuitable as health-related environmental indicators. In particular, they are only partially health-related and provide a very poor guide to health-related environmental exposure; only 2 out of 233 indicators relate specifically to exposure. There is therefore a need to develop indicators specifically for health-related aspects of the environment. In particular, these indicators should be based on current environment-and-health policy priorities and known epidemiological relationships. They should also be assessed to ensure that they provide a representative picture of healthrelated environmental exposure and their compliance with the HREI selection criteria should be examined. 162
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2. United Nations. Earth Summit 92: The United Nations conference on environment and development. London, Regency Press, 1992. 3. Department of the Environment. The UK environment. London, Her Majesty's Stationery Office, 1992. 4. Ministry of the Environment. Repurt on the state of the environment in Italy. Rome, Instituto Poligrafico e Zecca dello Stato, 1993. 5. Bakkes, J. et al. An averview ofenvironmental indicators: state of the art and perspectives. Nairobi, United Nations Environment Programme, 1994. 6. Jarman, B. Identification of underprivileged areas. British medicaljoumal286:1705-1709 (1990). 7. Townsend, P. Deprivation. Journal of social policy 16(2): 125146 (1987). 8. Kent, D. et al. Coupling wetlands structure and function: developing a condition index for wetlands monitoring. In: McKenzie, D. et al (eds) Ecological indicators: Volume 2. London, Elsevier Applied Science, 1992, pp 559-570. 9. Ludwig, J. &: Tongway, D. Monitoring the condition of Australian arid lands: linked plant-soil indicators. In: McKenzie, D. et al (eds) Ecological indicators: Volume 1. London, Elsevier Applied Science, 1992, pp 765-772. 10. Anderson, V. Alternative economic indicators. London, Routledge, 1991. 11. Life in Jacksonville; QJ.tality indicators for progress. Jacksonville, F1orida,Jacksonville Community Council, 1993. 12. Alexander, L. Health-related indicators for a sustainable community. Lancaster: Environmental Epidemiology Research Unit, Lancaster University, 1994. 13. Environmental indicators. A preliminary set. Paris, Organisation for Economic Cooperation and Development, 1991. 14. Core set of indicators for Environmental Performance Reviews: a synthesis repurt ffy the group on the state of the environment, Environmental monographs No. 83. Paris, Environment Directorate, Organisation for Economic Co-operation and Development 1993. 15. Ministry of Housing, Spatial Planning and the Environment, The Netherlands. National Environmental Policy Plan 2: Summary. The Hague, Department for Information and International Relations, 1994.
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163