THE POPULATION STRESS INDEX, AND SOME SOLUTIONS

Posted on March 2, 2004 by Dave Pollard

In order to test Edward Hall’s hypothesis that population stress is the fundamental cause of human violence and war, I decided to see if there was a correlation between the state of civil unrest and the density and growth of human population in various countries around the world. Using data from the FAO, I computed the population per arable hectare of land for each country in the world with at least a quarter of a million people. Then, using data from the Population Reference Bureau, I mapped this to annual population growth rates (%) for these countries. Initially, I produced the scatter diagram shown below:
scatter chart
In this chart, about a third of the countries, those with annual growth rates under 0.5%, are excluded to keep it from being too busy. The overall global population per arable hectare (4.0) and overall global annual growth rate (0.8%) are shown by a large blue dot. The sustainable global population per arable hectare (1.0, per a variety of sources I have cited in earlier posts) and the sustainable overall global annual growth rate (0%) is shown by a large green dot. No country has achieved that sustainable level — every country in the world has either positive growth rate or a density over 1 person per arable hectare.

Sure enough, the countries furthest from the green ideal point are also, almost without exception, the most violent and war-torn countries. At the far extreme, you find Palestine and Kuwait, with Saudi Arabia, Israel, Egypt and most of the MidEast countries close by. In the upper central part of the chart you find most of the war-ravaged sub-Saharan African countries, led by the Congo, with its horrendous and incessant war, Sierre Leone, where militias amputate their enemies’ limbs as a symbolic warning, and Rwanda & Burundi, site of the bloodiest massacre of the last half-century. Here, too, you’ll find Colombia, where anti-drug spraying and civil war have killed thousands, destroyed the economy and poisoned 80% of the arable land. And you’ll find Haiti, site of this week’s coup, and several Central American states that have witnessed horrendous warfare in recent years.

I then decided to multiply the two factors — density and growth — together to produce what I call the Population Stress Index (PSI). The calculations are shown graphically (I have tables if anyone wants them as well) on the map above: Purple for a PSI over 10 (extreme), Red for 4-10 (very high), Orange for 2-4 (high), Yellow for 0.5 to 2 (moderate), and White for less than 0.5 (low).

If you were to correlate this index against the propensity for violence and war in the past few decades, I think you’d find a nearly perfect match. What’s more interesting is that if you repeat the exercise using data from a century ago, you find the major belligerants of the world wars have the highest scores. By the middle part of the last century, China, Vietnam and Korea had exceptionally high scores.

So what can be done to bring annual growth down to, and below, zero, to achieve globally a zero PSI, a situation that today exists nowhere on Earth? In his essay How to Influence Fertility, John R. Weeks, Director of the Population Center at San Diego State University suggests the following programs to reduce population growth, and ultimately reduce global human population to the sustainable level of one billion, no more than one person per arable hectare:

	Direct Programs	Indirect Programs
Enabling Rational Choices	Provide full legal rights to women Increase legal age at marriage for women	Promote secular education Promote communication between spouses
Providing Motivation	Payments for not having children Priorities in jobs, housing, education for small families Community improvements for achievement of low birth rate Higher taxes for each additional child Higher maternity and educational costs for each additional child (“user fees”)	Economic development Increased educational opportunities for women Increased labor force opportunities for women Peer pressure campaigns Lower infant and child mortality rates Child labor laws Compulsory education for children Peer pressure campaigns
Making Means Available	Legalize abortion Legalize sterilization Legalize all other forms of fertility control Train family planning program workers Manufacture or buy contraceptive supplies Distribute birth control methods at all health clinics Make birth control methods available through local vendors Establish systems of community-based distribution	Public campaigns to promote knowlege and use of birth control Politicians speaking out in favor of birth control

It’s certainly a solution set worth striving for. I am, however, pessimistic that it’s sufficient to overcome the enormous population momentum that I’ve written about on these pages. Nor do I have much confidence that, when we have an American regime that is hell-bent on banning abortion again, which deprives foreign aid and support to countries and agencies that practice family planning, and which funnels money to religious groups hostile to birth control, there will be enough political will or economic investment worldwide to bring these programs to fruition.

You would think that, when evidence indicates that overpopulation is the key cause of environmental degradation, violence and war, and human suffering, there would be an unstoppable groundswell of support for programs to reduce our population back to sustainable levels. But that’s the power of our culture: In the face of irrefutable proof of its folly, we continue to chant the mantra of Growth.

Postscript: 3pm — Just found this interesting site from Matthew White, who tabulated the death rate from war and atrocities during the period from 1975-2000, and conveniently mapped it like I did the PSI. His colour code is: bright red over 1% of the population (extreme), dark red 0.1-1% (high), maroon 0.01-0.1% (moderate), black under 0.01% (low):
war deaths map
Sure looks like a close correlation to PSI to me. I’ll have to go back and plug in his data to my table to calculate the r² correlation coefficient, but I’m willing to bet it’s very high.

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18 Responses to THE POPULATION STRESS INDEX, AND SOME SOLUTIONS

Ken Hirsch says:

March 2, 2004 at 08:54

A tremendously unconvincing post. It would be nice if you tried to make a scatter plot between your “population stress index” and any measure of violence. Or, for wars, you could divide the countries into two groups, those that have had wars in the last (say) twenty years and those that have not.You might also want to distinguish, when possible, between aggressor states and non-aggressor states. Kuwait did not invade Iraq in 1990, after all, so it’s bizarre to try to link the war to Kuwait’s population. Simply mentioning a few from the beginning or middle of the twentieth century is not really helpful. Most countries were involved with war during that period. There were two world wars.In some cases the direction of causation is not clear, either. Palestinian women have been called upon to have many children to aid in their struggle. The Israeli Prime Minister in 1986 called on Israeli children to respond by having 4 or mor children.There has actually been research on this question. It’s been a couple of decades since I read about it, but if I recall correctly, there’s no simple link between population and violence.
Sherri says:

March 2, 2004 at 12:15

In psych 101, maybe it was sociology, the professor talked about a test done on rats: the more rats put into a confined area, the more violent they became. We didn’t study this in detail, so I don’t know/remember if all the groups were given the same amount of food/water.But I don’t need to see any studies to connect population and violence; if there’s not enough food or water (potable, non-toxic), it makes sense to me there’d be violence.
Dave Pollard says:

March 2, 2004 at 12:32

Ken: I’ve added a postscript and map that I hope will address some of your doubts. It’s not population per se that correlates to violence, it’s density, growth rate, and the availability of arable land. I think Hitler, whose Germany had a huge PSI through the first half of the 20th century, called it ‘living space’. I’d be interested in reading the source you recall that claimed there was no direct correlation; sounds very Lomborgian to me ;-)
Dave Pollard says:

March 2, 2004 at 13:02

Sherri: Great blog you have! — Beautiful design and excellent, original content.
Ken Hirsch says:

March 2, 2004 at 14:32

Lomborgian? You haven’t even shown a correlation coefficient and yet you claim to have “irrefutable proof”! I hope you do read Simon and Lomborg; they have interesting perspectives on things.If you’re really interested on the relationship to war, here’s a syllabus for a graduate course: http://www.rci.rutgers.edu/~jacklevy/522SyllabusSp2003.pdf.It has lots of stuff about environment and population.
Dave Pollard says:

March 2, 2004 at 15:49

Ken: Now you’re just being argumentative. My statement about “irrefutable proof” was regarding the folly of our society’s belief in perpetual growth, not the correlation between war and population stress. That kind of misquote borders on malice, and I don’t appreciate it. And if you’d think for a minute, you’d realize that a correlation coefficient on this data would be at best persuasive anyway — the PSI is a predictive model, not a historical one: PSIs today should correlate to wars in the next quarter century, and Matthew’s data should correlate to PSI’s as of 1975. If I wanted to write a thesis I’d go back and do that sort of research, but the maps are compelling enough for me. As for Simon and Lomborg, I have read them, and they’re both absurd. Lomborg has zero credentials in the subject he writes about, and has been debunked by a small army of scientists who do. As for your syllabus, I have no idea why you linked to it — it’s 97 pages of mind-numbing, interminable deading lists, of which only one reference — that to the dubious Simon — has any relevance whatsoever so the correlation between overpopulation and violence.
Ken Hirsch says:

March 2, 2004 at 17:35

If you want us to believe your model has predictive power, you have to validate in some way, such as against historical data. You haven’t convinced me at all.I gave the link to the syllabus in case you were really interested in the complicated truth. The relationship between population and war or crime or the enviornment or quality of life is complex, not simple.There’s plenty in the syllabus that’s relevant:Thomas Homer-Dixon and Jessica Blitt, eds., Ecoviolence: Links Among Environment, Population, and Security. Lanham, MD: Rowman & Littlefield, 1998.Thomas F. Homer-Dixon, Environment, Scarcity, and Violence. Princeton: Princeton University Press, 1999.Nazli Choucri, ed. Multidisciplinary Perspectives on Population and Conflict. Syracuse: Syracuse University Press, 1984.Sam Sarkesian, “The Demographic Component of Strategy.” Survival 31/6 (1989): 549-64.Nicholas Eberstadt, “Population Change and National Security.” Foreign Affairs, 70/3 (Summer 1991): 115-21.Pierre DeSenarclens, “Population and Security.” International Social Science Journal 46,3 (1994): 439-54.Jack A. Goldstone, “Population Growth and Revolutionary Crises.” In John Foran, ed., Theorizing Revolutions. London: Routledge, 1997. Pp. 102-120.Julian L. Simon, “Paradoxically, Population Growth May Eventually End Wars.” Journal of Conflict Resolution 33/1 (March 1989): 164-80.Colin Kahl, “Population Growth, Environmental Degradation, and State-Sponsored Violence: The Case of Kenya, 1991-93.” International Security 23, 2 (Fall 1998), 80-119.Clement A. Tisdell, “Population, Economic Change, and Environmental Security.” In Nicholas Polunin, ed., Population and Global Security. New York: Cambridge University Press, 1998. Pp. 93-116.Nana Poku and David T. Graham, eds., Redefining Security: Population Movements and National Security. Westport, Conn.: Praeger, 1998.Ronald R. Krebs and Jack S. Levy, “Demographic Change and the Sources of International Conflict.” In Myron Weiner and Sharon Stanton Russell, eds., Demography and National Security. Providence, RI: Berghahn Books, 2001. Pp. 62-105.
Pat says:

March 2, 2004 at 18:05

Frankly, the rapid rates of population growth in parts of the world are appalling to me. I don’t even CARE if there’s a correlation with violence. The population increases have done great damage to the planet. Now, perhaps if extreme violence occurs due to the resulting stresses, we will see some of the excess population killed off. I would like to say how much I would miss them, but . .
Kevin says:

March 2, 2004 at 22:33

Although Dave mentioned it, it seems that the third factor “availability of arable land” gets a little lost in the graphs and maps. And even then there is something else missing, not sure what though.Although not as densely populated as some of the countries you mention, Tokyo ranks fairly high up there I would assume. And although Japan does not have a great deal of *local* land available for agriculture, they have the economic means and access to arable land in other parts of the world. This obviously goes a long way to relieve the stress of so many people in so small a place.But even so, relative to even less-dense locations in first and third-world countries, the violent crime rate in Tokyo is almost nonexistent.While I haven’t spent a long time trying to research what factors make Japan an exception, off the top of my head I would venture to say it has to do with the “one class-ness” of Japan. It is often said that Japan really only has a middle class, and relative to other nations, this is true.Japan also does not have a strong religious position. Not to say that there are not religious people, but generally even the religious people are very tolerant of other religions. (Bhudist by day, Christian wedding, Shinto burial)Not to say that I think it is good, or that multi-racial groups are bad (I would love to see a more diverse Tokyo), but I think that a big factor is that Japan is mostly ethnically Japanese people. (There is racial tension growing now as Japans population is on a decrease, and the economy will need more foreign labor. There is also an extremely racist mayor of Tokyo who if he had his way, would see the chinese and koreans deported. You can bet that might stir up some violence.)Then there is the whole “nail that sticks up gets hammered down” thing. Although it is changing, compared to the US, it’s seems spot on. I shudder to think what life would be like in Tokyo if there were greatly divided economic classes, filled with individualistic, racist, religious fanatics. — and limited access to affordable imported food.
Kevin says:

March 2, 2004 at 22:53

I should clarify. I ralize that Japan as a country may not be one of the countries that makes your chart, but I was thinking along the lines that the correlation should hold somewhat true even in the less-dense, less-violent lower spectrum of the chart.If it doens’t, then it would be interesting to see where the point is that the correlation ends, and density, land, and growth rate are not longer a factor, and why.
Dave Pollard says:

March 3, 2004 at 00:00

Kevin: You mean is there a ‘tipping point’? That’s an interesting point, and the areas that would be the perfect tests for that hypothesis are North America and Japan. In both Canada and the US the current density per arable square mile is relatively low, but, due almost entirely to immigration (and the propensity of new immigrants to continue for a couple of generations to have large families), they both have growth rates above 1%, higher than the global average. On the other hand, while Japan has a higher density, it has a much lower growth rate, which is why it’s in the same PSI category as North America. If there’s no tipping point, the countries that are yellow on my map should have no higher rate of violence than the countries that are white. The US does have a higher rate of murder, violence and incarceration than most of Europe, but neither Canada nor Japan has. But if you project ahead, by 2100 there could be as many as 1 billion Americans and 100 million Canadians, and due to the excessive sprawl in North America such a population jump would essentially eradicate all agricultural land in North America, putting both countries into the red (very high) PSI category. I can easily imagine a huge increase in violent deaths and imperialistic wars under such a scenario, with cities the size of small states and a massive scarcity of natural resources. Japan, on the other hand, will according to current projections actually decrease in population by 2100, shifting from the yellow to the white (low) PSI category. So it may be that growth rate is more important than current density, and its correlation with future violence commensurately higher. You also raise an important point about the ability to ‘extend’ one’s arable land by appropriating one’s neighbours’. In past centuries that was war, but nowadays you can accomplish the same thing by economic imperialism, essentially ‘stealing’ land from another country, reducing their people’s available land and adding it to your own. Kind of like immigration in reverse. There’s also been some research that indicates that high economic disparity in an area increases crime rates, and vice versa, which would be a mitigating factor for Japan and an aggravating one for the US.
KevinG says:

March 3, 2004 at 20:44

Dave-An interesting post. If there is a correlation that plays out I think there is still a need to demonstrate a causal relationship. I’m not arguing the general principle that unbridled growth is unsustainable but how do you go about demonstrating that the violence is caused by the psi factors. It could easily be the case that both the violence and the psi are caused by something else like failed governments who inherited insurmountable problems from colonialism for example.
Dave Pollard says:

March 3, 2004 at 23:10

KevinG: Good point. Suppose I demonstrate that there is a high correlation between 1975 PSIs and subsequent death-by-violence data. To me that strengthens the argument for causality and lessens the likelihood of mere coincidence due to another co-determining factor. But you’re right, it doesn’t eliminate the possibility. I don’t know if it’s even possible to eliminate that possibility, although comparing the correlation of other competing causal hypotheses might reduce it. This was just an intellectual curiosity to me, so there’s a limit to how far I’m prepared to take it, but if someone else were to show a comparable correlation between some other factor and violent deaths, I’d certainly take a look at it.
KevinG says:

March 4, 2004 at 09:32

Dave-It is an intellectual curiosity for me as well. The origins of systemic violence is something I have thought about for some time. A post some time ago talking about income disparity vs objective poverty driving crime caught my attention.The conclusion I have come to – more of a non-conclusion – is that there are several inter-related drivers and that cause and effect are difficult to separate. Is the low PSI a result of prosperity which rduces violence or is the high PSI creating the violence. Is democracy required to lift people out of poverty or does democracy require a level of prosperity before it can flourish.The answer to these questions always seems to be yes.
Aalia Wayfare says:

March 4, 2004 at 13:17

A useful technique to apply here might be factor analysis. If you broadened out your variables to include a range of factors that might explain societal instabilites eg currency fluctuations and climate measurements it should be possible to see if the are loadings on particular combinations.Others here have questioned a simple realtionship between population and war but this should be simple to test. It seems likely in advance of analysis that the interrelationships will be complex but I can’t see why they would be impossible to evaluate.I suspect that the clincher for the argument would be to perform confirmatory factor analysis where you specify in advance the expected factor loadings and test to see if the correlation matrix is producable from your hypotheses.While the results of such analysis would undobtedly be interesting, I do think that proving casuality is one of the hardest things to achieve using statists. What they can give us though are hard probablilities about the likelihood that there is a relationship between the factors being studied.Refs: http://trochim.human.cornell.edu/tutorial/flynn/factor.htmand http://www.statsoftinc.com/textbook/stfacan.html are useful introductions
Aalia Wayfare says:

March 7, 2004 at 15:24

I really hope that comment didn’t sound critical. I think its really clear that Dave’s PSI is going to be a strong predictor. My personal interest would be in understanding the psychology of nations that were experiencing high PSI but still don’t tip over into wholesale violence.Best Wishes
Don Dwiggins says:

March 8, 2004 at 11:42
Dave Pollard says:

March 8, 2004 at 13:34

Don: Any economy that relies on continued ‘natural’ population growth forever is a model for disaster. What’s needed isn’t a study of population decline (that’s inevitable, one way or another) but a study of how to wrench the economy free of its thirst for endless growth and create a new one based on sustainability.