Dear Jean-Philippe, 

You can find some examples of constructing such synthetic indicator of SD in our article "Sustainable development assessment: quality and sustainability of life indicators at global, national and regional level" (Foresight, 2003 - you can download it below). In this article some other indicator methodologies are also cited. Surely, some other approaches for constructing complex statistical indices were developed last years - I can look for some of them, if you are interested. 

Article Sustainable development assessment: Quality and sustainabili...

‘Systems thinking’ approach provides the tools that can highlights and addresses problems using integrated approaches and it demonstrate how to translate difficult ideas into potent management tools for change. The evidence of successful systems thinking application can be seen in various fields and disciplines exploited by many researchers, managers and policy makers in African. With it associated tool such as the Bayesian Belief Network modeling, it satisfies the ‘Bellagio Principles’ for measuring sustainable development indicators. Try it. Depending on which context sustainability is seen from inter played with social, economic, cultural, environment and politics, may vary with it associated indications, and in the first place any indicator of sustainability not look at from interconnected or systemic points of view will not and can not give you clear or all the indicators or holistic view of the entire system that can be altered with small changes in its leverage points. Please read more on Bayesian Belief Network modelling and the Systems thinking approach

Regards,

Banson

try to learn or adopt from van Loon book. the title of the book is Agricultural Sustainability. Inside, there is indicator of sustainability (economy, social, and environmental) and the model.

In my view it is not so useful to think of sustainable development as a balancing act involving economic, environmental and social goals. There is more to gain from a more hierarchical view as proposed by ecological economist Herman Daly. He explains that sustainable scale, equitable distribution and efficient allocation are three independent, incommensurable goals of sustainable development. First step is to decide on how much of the Earth's resources we can use. Second step is to decide on the distribution of these resources: who has the right to use or own them? Third step is to decide on how people can exchange what they have in order to fulfill their needs, for example through a market mechanism.

Any 'synthetic indicator' should in my view reflect this hierarchical relationship between these three goals of sustainable development. Herman Daly and others have developed a range of ideas in this direction, e.g. around 'uneconomic growth'. Perhaps worth a look.

http://www.sciencedirect.com/science/article/pii/092180099290024M

Kenneth, I agree that all of these decisions are fundamentally political. My point is that there is a certain hierarchy in the issues. Humanity needs a favourable natural environment, so there are certain ecological limits to what we can do. Next: economic activities take place in the context of a certain distribution of wealth and income. Market outcomes can be fundamentally different with a different initial distribution of wealth and income. Ecological limits matter, distribution matters, efficiency matters. And given the incommensurabiliity of these issues, subsituting one for the other is fundamentally problematic. That is my point. The fact that the ecological limits are difficult to establish and that what is equitable is highly subjective does not mean that we should ignore these issues all together and assume everything can be traded-off. 

Dear Jean-Philippe,

Well, your question has many technical problems associated, such as agreeing what is SD, weighting the different components of this SD, elaborating a synthetic indicator or compiling enough information to quantify this indicator. But I am convinced that technically everything is possible in this field. In fact, many solutions have been proposed from monetary or biophysical approaches (e.g. ecosystem services approach, goal functions, etc.).

But I think that the main (and in my opinion irresolvable) bottleneck is intrinsic incommensurability of value associated to sustainability, as Mr. Amelung discussed before. Society, Ecosystems or Economy belong to different descriptive domains (different spatial and temporal scales, different functioning, different goals, different components, etc), and cannot be compared and summed within a unique indicator. Trying to include everything about one of these descriptive domains in one indicator has continuously leaded to meaningless numbers. One of the examples can be the interpretation of GDP in Economics as the single indicator of growth.

Notice that I do not say anything about taking decisions on sustainability. There are many works on Multicriteria Assessment explaining how to elaborate processes of decision-making in complex situations like this (you can search for Giusseppe Munda or Mario Giampietro for specific references) by using different sets of indicators and social techniques for participation and governance.

Good luck.

Dear Jean-Philippe

Combination or aggregation of indicators usually produces indexes, oe os the most known is Human Development Index, that brings together literacy (or average years of edcuation), health, and income. To build indexes require you have not only sound concepts on what you want to measures, but balanced weights for each component of the index (also known as indicator). You can employ Analytical Hierarchy Process (AHP) or any type of procedure that delivers the proportionality of the indicators. I agree with Dr Pedro that people and consensus achievement for how to build indexes is a pivotal question, because sustainability depends mainly on what people desire to sustain. However, indexes, as long as they represent aggregate information, are not so suitable for small scale assessments. I suggest you to look at  Ecological Economics journal, they publish several articles on this subject.

Dear Jean Philippe

I mostly agree with Mr Lomas and Mr Kennet and I also suggest you to read about the debate and the achievements related to "going beyond GDP" in EU works and by OECD, UN, World Bank and others.

As explained in previous discussion - common denominator for all these categories could not possible be determined. Indexing policy is often questionable. We have somewhat different approach. Everything we do, develop, create,... we do for a purpose. Hence lets start from purpose. One develops goal driven matrix, define priorities with stakeholders, checks interactions and than decide what to do. One point, though, will always be something we can not be certain about. Sustainability, in any of its categories, does not have constant value. They are dynamic categories - what is sustainable today might not be as sustainable tomorrow. In that field we try to arrive to projections rather than use today's merits.

It is obvious that the problem is of multiple objective nature. One can produce a pareto set and then analyze the trade offs that exist between the three objectives, economic, social and environmental optimum. The use of weighting factors can give a single function that combines all the objectives.

Check this book by OECD and JRC of the European Commission...

http://www.oecd.org/std/42495745.pdf

I agree with many of the previous commenters, but would like to add one thought. It seems to me like a more fundamental question is why are you looking to combine sustainability criteria into a single index? By answering this question, I think you will come to realize that there is not one method which can be considered correct (only different methods for different contexts). The information that is being conveyed is much too complex to be gleaned from one value. One socities '95' could easily be another societies '35', and no one would be able to tell either that they are wrong. This comes because each society has different values and preferences, and multi-criteria problems require some preferences to be obtained before a final solution is reached (assuming Pareto optimality among the solutions).

On the other hand, in my field (infrastructure) sustainability assessment systems have helped to increase awareness for actions and activities by creating a single 'sustainability score'. As the contractors seek a label for their project which deems it as sustainable (good marketing), they are forced to review their actions and decisions along the way in order to benefit the triple bottom line. Therefore, as the contractors seek the single sustainability index or score, the journey required to obtain the score becomes more important than the final number.

Once again, I urge you to revisit the question, "why do I need one single number to represent sustainability?" If the single number approach is truly what is needed, then I encourage you to read through some of the previous recomendations, as well some of the work done on tradeoff's for sustainable development or ecological economics (e.g., Nick Ashford, P. Soderbaum, etc.). 

Dear Jean-Philippe, you can also read the Jacques Richard's book (in French) "Comptabilité et Développement durable" (Economica, 2012) to find some examples of such indicators and their critical analysis.

HI Antoni, I think Multi-Criteria Decision Analysis Techniques (MUVT, Elimination, PROMETHEE, AHP etc.) can be used as a tool to develop composite indicator from social, economic and environmental indicators. It can use any kind of numerical data, and the results of the analysis can be utilized to interpret the importance of the different indicators in the overall sustainability score. It deals with criteria incommensurability, data uncertainty and preference imprecision. It allows to bring indicators into common scale otherwise  comparison is difficult unless the separate indicators are transformed into some common form.

You can also use modified HDI framework to generate composite index.

In the context of taxation, especially border carbon tax (BCT) of nations, reducing various indicators to a single number is important. IMHO, more than accuracy of the combination, selection of robust and complementary indicators could play a key role in adaptation among developed and developing nations with heterogeneous and contradicting features. As an example, we used GDP, frozen population, and IHDI indicators to develop a consistent indicator of activities across nations, which is then used to introduce a generalized GHG Intensity indicator. The advantage of this modified GHG Intensity indicator is that it brings all nations to a comparable scale (BCT of China and USA is calculated 4.5% and 1.6% respectively in the IIGHGINT version) without requiring any debate or forfeit, in contrast to the regular GHG Intensity and GHG per Capita indicators. Although it might not be a fully accurate indicator or combination, it could serve as a starting point of an agreement. Please see below for more details:

Chapter IIGHGINT: A generalization to the modified GHG intensity uni...

Article A Modified GHG Intensity Indicator: Toward a Sustainable Glo...

Kenneth...with all the respect, I have to disagree. Maybe from a literal point of view, the term 'frozen' that I used in the previous answer was misleading, but that is not the point. We started with the 'total population' of nations in 1990 as defined and reported by the World Bank. Then, we used these 1990 total populations as constant for the following years, and the resulting indicator was called the 'snapshot' population (I apologize in-advance if the literal meaning is something else).

The reference year was set to 1990 because i) this year is associated with the start of many environment-friendly efforts (it was wisely suggested by an anonymous reviewer), and ii) the status of many nations seems to be in a semi-robust state in that period of time. However, the whole purpose was to have a proof of the concept, and the reference year could be modified or even be generalized to be period of time.

The population challenge is much more serious compared to other challenges, such as that of climate change. Therefore, if an indicator implicitly 'promote' increase in the population, this could easily lead to exploitation especially in less developed regions. The indirect damage of such an indicator would be much higher than its benefits. Recently, the UN had to correct its estimation of the world population in 2100 from 9 billions to 11 billions. Moreover, in some regions, the population has been doubled or tripled only in the last 30 years. This shows that there is a high degree of instability and risk. This has been the main reason that we decided to develop and use the 'snapshot' population variable back in 2011.

From the subjectivity criterion, I do not see any difference between setting 1990 as a reference year or choosing the first 50 years of the last century as a reference period. Maybe for a specific region the data of that 50 years is available, but many regions even have not been discovered at that time. Even if we limit the scope of the study to only that region that its data is available, and if we assume that a model could be hypothetically developed that is 'accurate' over that period of time, the differences in the society, the technology, and especially the powerful (also mentioned above in a good comment on the role of policies) between the current time and that period of time (a 100 years before) could be so high that the portability of that model to the current time could neither be guaranteed nor be validated.

Kenneth. I have respect for your perspective. However, I do not see any direct link between what you said and the modified GHG intensity indicator I was talking about. I summarize that indicator below for the purpose of clarity, and I will try to avoid using extra words.

1. When a change in behavior is planned to be induced or engineered using an indicator, it is important to prevent any potential side effect. The purpose of the proposed GHG intensity indicator was to provide a way for 'resource' management among nations, in particular the GHG emission resource (maybe calling it global GHG emission 'budget' is more meaningful). The side effect that we observed was a potential positive feedback on the population growth. Therefore, the indicator was engineered in such a way that it nullifies such a potential positive feedback. Therefore, there is no claim that: i) this indicator will control or freeze the total population, or ii) there is a direct relation between the total population and the CO2 level.

2. I describe the IPGHGINT indicator here. You can read the details of the IIGHGINT indicator in the paper.

3. IPGHGINT is about 'resource' management especially when a resource is limited. We applied the concept to the GHG emissions in these papers, but it could easily be generalized to other resources.

4. IPGHGINT works based on resource 'allocation' according to 'credit' of the nations. Therefore, it will not be a blocker for the nations; they are free to perform the way they believe is the best in a year, and then at the end of the year their credits is calculated, and accordingly penalties (border taxes, for example) is set for the next year.

5. IPGHGINT assigns the credits based on the 'activity' of nations in a year.

6. The activity of a nation is defined as the sum of two parts: its measurable activity (in terms of the GDP) and its hidden activity (in terms of the product of the IHDI and the total population):

IHDI is the Inequality-adjusted HDI or in full Inequality-adjusted Human Development Index. We argued that depending on the level of development (captured by the HDI), the hidden activities could be measured. Then, we moved one step further to IHDI because it is well known that in many regions the development is not well distributed among the population. Therefore, the powerful of a nation could not take credit of its heads (or feet), if they do not provide the same level of development or quality of life to all residence.

7. That is the end of the definition of the indicator. However, to apply it we need to have the 'limit' of the resource set. In other words, the budget should be set by another process, and then the indicator could be used to 'allocate' the resource. In these papers, we used the IPCC scenarios because they were ready and well-known. However, it does not mean that the indicators are attached to those scenarios. Anybody, including you, could proposed a yearly budget (actually two yearly budgets, one for the upper-bound and another for the lower-bound), and we can re-calculate the indicators and BCTs accordingly.

8. As you also implicitly mentioned in your comments, the world is an ecosystem (not in a literal way) of various actors. The notion of 'control', which is popular in the Systems Science, is meaningless for an ecosystem, and it is the 'management' that could help in guiding that ecosystem toward development and sustainability.

9. Finally, it is worth to mention that Risk is not all about Climate Change, Climate Change is not all about GHG Emissions, and GHG Emissions is not all about CO2 Level.

Dear Jean-Philippe,

My input is addressing sustainability indicators for cities.

On a conceptual point of view, you may consider the following issues :

i) There is a necessary trade-off between scientific and policy interests when building you index. Experiments show that in terms of sustainability, the production of indices based on a purely scientific approach tends to ignore or underestimate the importance of the political dimension. This would explain why these indices fail to gain legitimacy among policymakers. On the other hand, approaches based on political consensus favour the participation of several stakeholders to define common goals and build indicators and indices. Such approaches introduce bias into the development of indices, which is denounced by scientists. For further discussion on this issue, please see: Rametsteiner, E., H., Pülzl, J., Alkan-Olsson et P., Frederiksen, P. (2010). Sustainability Indicator Development: Science or Political Negotiation? Ecological Indicators [doi:10.1016/j.ecolind.2009.06.009]

ii) Simple is good, as long as it is transparent. For further reading on this issue, please see: Singh, R.K., Murty, H.R., Gupta, S.K. et Dikshit, A.K. (2009). An Overview of Sustainability Assessment Methodologies. Ecological Indicators, 9, 189-212.

On an operational viewpoint, you may consider these readings:

i) Nardo et al. (2008). Handbook on Constructing Composite Indicators: Methodology and User Guide. OCDE, ISBN978-92-64-04345-9. You will find different approaches to build indices.

ii) Maclaren, V.W. (1996). Developing Indicators of Urban Sustainability : A Focus on the Canadian Experience. Toronto : Intergovernmental Committee on Urban and Regional Research Press, January.

Finally, I am writing a thesis which is addressing: i) The Interpretation of Sustainability Indicators and Indices Following their Measurement and ii) The Methodological Issues Affecting Sustainability Rating of Cities. Let me know if this is something that could be helpful in your research.

Best regards,

Juste

Kenneth...Your point about the relation between CO2 and population deserves its own question/answer thread.

1. Cautions should be taken when statistical inference based on historical data is carried out:

1.a Over-aggregation: Population growth could be dominant in Region I while the CO2 emissions are independently dominant in Region C without any direct relation. When aggregated at the world level, they would appear as correlated, which might not be correct.

1.b Nonlinear regimes of systems: Projection of relations inferred from historical data collected from the linear regimes would be highly off the confidential interval of actual behavior when the system enters nonlinear regimes.

2. Carbon soot (black carbon) seems to play a role in melt down of ice while it is not listed as a GHG.

3. Methane and N2O have considerable shares in the global GHG emissions. Therefore, CO2 is not alone.

4. In general, physical systems do not behave according to the world opinion.

Kenneth.

3. Your point about a possible relation among i) GHG Emissions, ii) GHG Levels, and iii) Global Population is interesting. However, as mentioned before, any relation at the global level should hold when disaggregated to a regional level. This discussion deserve its own question. That said, GHG emissions are not limited to burning fuels. Agriculture and Land Use are two other well-known sources of GHG emissions.

4. I am not sure how we can define the 'world opinion', how to measure it, and how much it would reflect the reality. However, if we switch to a global (world-level) 'agreement', it could be defined. Nonetheless, a global agreement would not guarantee presence of a coherent global opinion (super-belief) at the back end. Also, similar to the world opinion, a global agreement would not have any 'direct' impact on the behavior of physical systems (the nature). However, it could be used as a 'tool' in 'management' of other parts of the "ecosystem", i.e., i) human (individuals), ii) societies, and iii) enterprises (businesses). Having a global agreement that is both i) well-thought and ii) global (without exceptions) could be leveraged toward a sustainable future. Again I think this point deserves its own question.

https://www.linkedin.com/pulse/20140807030921-60666930-sustainability-pentagon

Dear Reza Farrahi Moghaddam,

The triple pillar [environment-economy-society] paradigm is obviously suffering from deficiencies with regard to description and discussion of global sustainable development. Therefore, your suggestion to add elements to the model is important. On the background of the discussion held in this forum it is evident that “global human population size” is THE cardinal factor to consider in any analysis of global sustainable development. Where, in which element of your model, is this factor residing?

Thanks in advance for your answer.

Dear Benjamin Steinitz,

Thanks. I will briefly describe the idea of the Sustainability Pentagon (SP) model and at the end will get to the population size.

1. Despite its name, the Sustainability Pentagon model does not explicitly offer any solution for sustainability. Instead, it is a framework for 'understanding' of the "ecosystem". Another layer of 'management' based on such an understanding could be built on the top of the SP model. The concept of 'responsibility' could be used for that management layer. Please see the MEIO model (the link below) for a simple case.

2. The SP model is based on 'actors'. In other words, there is no 'pillar' in such model. Instead, there are five 'categories' (which could be extended to a higher number in future) that cover all actors involved. For example, the category of 'nature(s)' covers all nature actors, such as a forest in northern Manitoba or a forest in southern Amazon. Each one of these actors have their actions:

3. The SP model is based on 'actions' (including inactions, i.e., not reacting to an event, a poke, or a nudge). The actions could be intra-category (for example, between two individuals) or inter-category (for example, between an individual and a natural resource (footprint), or between an enterprise and a society (contribution )).

4.a The 'population size' of every actor has an implicit impact on the strength of its actions. Banning plastic bag in a mega city has bigger impact than a similar action in a small town (if for a moment we ignore the case of collective actions of many towns, and limit ourselves to a single-actor example).

4.b However, the population size is not the sole determinant factor. In an 'under-developed' society, the strength of an action could be much less than that of a developed society of the same population size. Therefore, the 'credit' that these two societies (as two actors) could receive for a similar action should be adjusted accordingly. This development-aware way of management would implicitly help to promote 'development' and 'equality' in all regions.

4.c A considerable portion of the global population is under-active. Therefore, the impact of their 'potential' fully-exploited actions in the future could be considerably bigger than that of current status quo, even if there would be no increase in the population size.

Article A Multi-Entity Input Output (MEIO) Approach to Sustainabilit...

How We Can Measure Sustainable Development: The Genuine Progress Indicator (GPI)

The GPI starts with the same personal consumption data that the GDP is based on, but then makes some crucial distinctions. It adjusts for factors such as income distribution, adds factors such as the value of household and volunteer work, and subtracts factors such as the costs of crime and pollution.

Because the GDP and the GPI are both measured in monetary terms, they can be compared on the same scale. Measurements that make up the GPI include:

Income Distribution

Both economic theory and common sense tell us that the poor benefit more from a given increase in their income than do the rich. Accordingly, the GPI rises when the poor receive a larger percentage of national income, and falls when their share decreases.

Housework, Volunteering, and Higher Education

Much of the most important work in society is done in household and community settings: childcare, home repairs, volunteer work, and so on. The GDP ignores these contributions because no money changes hands. The GPI includes the value of this work figured at the approximate cost of hiring someone to do it. The GPI also takes into account the non-market benefits associated with a more educated population.

Crime

Crime imposes large economic costs on individuals and society in the form of legal fees, medical expenses, damage to property, and the like. The GDP treats such expenses as additions to well-being. By contrast, the GPI subtracts the costs arising from crime.

Resource Depletion

If today’s economic activity depletes the physical resource base available for tomorrow, then it is not creating well-being; rather, it is borrowing it from future generations. The GDP counts such borrowing as current income. The GPI, by contrast, counts the depletion or degradation of wetlands, forests, farmland, and nonrenewable minerals (including oil) as a current cost.

Pollution

The GDP often counts pollution as a double gain: Once when it is created, and then again when it is cleaned up. By contrast, the GPI subtracts the costs of air and water pollution as measured by actual damage to human health and the environment.

Long-Term Environmental Damage

Climate change, ozone depletion, and nuclear waste management are long-term costs arising from the use of fossil fuels, chlorofluorocarbons, and atomic energy, respectively. These costs are unaccounted for in ordinary economic indicators. The GPI treats as costs the consumption of certain forms of energy and of ozone-depleting chemicals. It also assigns a cost to carbon emissions to account for the catastrophic economic, environmental, and social effects of global warming.

Changes in Leisure Time

As a nation becomes wealthier, people should have more latitude to choose between work and free time for family or other activities. In recent years, however, the opposite has occurred. The GDP ignores this loss of free time, but the GPI treats leisure as most Americans do—as something of value. When leisure time increases, the GPI goes up; when Americans have less of it, the GPI goes down.

Defensive Expenditures

The GDP counts as additions to well-being the money people spend to prevent erosion in their quality of life or to compensate for misfortunes of various kinds. Examples are the medical and repair bills from automobile accidents, commuting costs, and household expenditures on pollution control devices such as water filters. The GPI counts such "defensive" expenditures as most Americans do: as costs rather than as benefits.

Lifespan of Consumer Durables & Public Infrastructure

The GDP confuses the value provided by major consumer purchases (e.g., home appliances) with the amount Americans spend to buy them. This hides the loss in well-being that results when products wear out quickly. The GPI treats the money spent on capital items as a cost, and the value of the service they provide year after year as a benefit. This applies both to private capital items and to public infrastructure, such as highways.

Dependence on Foreign Assets

If a nation allows its capital stock to decline, or if it finances consumption out of borrowed capital, it is living beyond its means. The GPI counts net additions to the capital stock as contributions to well-being, and treats money borrowed from abroad as reductions. If the borrowed money is used for investment, the negative effects are canceled out. But if the borrowed money is used to finance consumption, the GPI declines.

I think it is unnecessary and hard to propose a comprehensive sustainable indicator that combines social, economic and ecological goals. But we can identify independent thresholds for  social, economic and ecological goals. Any sole goal can be relatively easy to identify and understand, such as water available. Moreover, the sole goal can be gained in the practice.

These indicators, by their character, could not be combined. But, on the other hand they are interlinked. For each particular location, project,... we have to identify interactions between each of these groups and their subgroups, quantify these interactions and, to make practical use of it, determine priorities based on specific set of particular criteria valid then and there.

At the macro level SDSN report on SDGs and the way to monitor and evaluate development based on them can be useful (link). 

At the corporate level you can check out sustainability indicators developed in the form of sets, indices, rating systems, etc. One of my articles cover this topic and there are several other studies cited in the paper (+the second article: application - bothattached). 

http://unsdsn.org/wp-content/uploads/2015/03/150320-SDSN-Indicator-Report.pdf

Article Designing a General Set of Sustainability Indicators at the ...

Article Developing a Fuzzy Corporate Performance Rating System: A Pe...

Dear Professor Towe,

Thanks for such incisive points. The sustainability discourse suggests that the initiators of sustainability are, just, the agents on change, however, the challenges ahead of us are humongous. The right approach to sustainability is not through enforcement, in my submission. What we need is a transformation, in short, change of attitude, change of mindset, and change of behavior. Not as simple as we put them next to each other. It takes a generation, at the best estimate. The global sustainability agenda has contemplated certain mechanisms part implemented since 2000 like the Decade of Education for Sustainable Development (DESD), part mentioned in THE 2030 AGENDA FOR SUSTAINABLE DEVELOPMENT, by UN, etc. yet these measures are still lacking because the diversity of cultures (how they would react to sustainability) and how it can be absorbed in each society has not been considered.

As far as a holistic (systemic) approach with the human interaction at its epicenter is not devised, these discussions would be to no avail.

Best,

Thank you for such perspicacious remarks.

Paris Agreement was a positive "political" step towards realizing the pressing issue of Climate Change, especially after the failures in Kyoto and Copenhagen in the past two decades. However, the most important part is the implementation. As you mentioned it is just the tip of the iceberg. Indeed, the interconnectedness and complexity of our problems are left unchecked. Though, we have the tools to overcome most of these problems. I read an interesting figure last week, which said that one year world military budget is more than enough to eradicate poverty in the world in one year. 

I especially like your question at the end and I think the answer is similar to the philosophy behind the What, the How and the Why questions in science. We know the "what" and even the "how" (at least potentially) but what we fail, so immaculately at, is in realizing the significance and meaning of "Why".

how about this one.

A new technique can use

PSO

meta heuristic aggregate weighted cost function

or multi objective functional defining

economic

social

environmental

and other cost factors I one or multi objective

using my fast convergent PSO

sharaf- self adjusting weighted search and optimization tool

please send me your email to send you my new

book chapter in Elsevier dealing with this technique.

[email protected]

we can test this nes indexing technique

Our own answer to the initial question is currently available here : https://authors.elsevier.com/a/1Y5jo7sfVYuL9n. Thank you all for your help !

https://www.researchgate.net/publication/340579524_C0MBINED_ECONOMY_MODEL_Developed_by_Rajitha_Medungoda_MBA_PhD_U_S_A_Managing_Director_Action_Valley_Campus