Happy Birthday Demography!

I received a note from Rich Lawler this morning, who passed along a note he received from Hal Caswell, who passed along a note he, in turn, received from someone at the Max Planck Institute for Demographic Research (where my friend Josh Goldstein is Director).  In this note, I was reminded that today is the 348th birthday of demography! You see, on this date (27 February) in 1661, John Graunt read his paper, "Natural and Political Observations Mentioned in a Following Index, and Made Upon the Bills of Mortality," to the Royal Society of London.  At the time of his writing, London had begun to keep track of the number of burials and christenings taking place within its jurisdiction.  In good empiricist Baroque British style, Graunt managed to extract an amazing amount of information from these data.  And this is really what demographers do to this day: we count things like births, deaths, and marriages and make inferences about the way the world works from these simple counts.

In this essay, Graunt mused about why one might want to do things like count deaths and births:

There seems to be good reason why the Magistrate should himself take notice of the numbers of burials and christenings, viz., to see whether the City increase or decrease in people; whether in increase proportionately with the rest of the Nation; whether it be grown big enough, or too big, etc.

Good practical reasons why one might want to count births and deaths. Perhaps the most notable thing that Graunt did in his essay is to construct the first life table, that mainstay of demographic analysis. Actually, at least one of life table actually existed in ancient Rome (attributed to Ulpian, 3rd century C.E.), but Graunt was certainly the first to write about a life table. He reasons:

Whereas we have found that of 100 quick conceptions about 36 of them die before they be six years old, and that perhaps but one surviveth 76, we, having seven decades between six and 76, we sought six mean proportional numbers between 64, the remainder living at six years, and the one which survives 76, and find that the numbers following are practically near enough to the truth; for men do not die in exact proportions, nor in fractions: from when arises this Table following:

Viz of 100 there dies within the first six years 36

The next ten years, or decade                          24

The second decade                                           15

The third decade                                                9

The fourth                                                          6 

The next                                                             4

The next                                                             3

The next                                                             2

The next                                                             1

 

With his radix set to 100, this means that "of the said 100 conceived there remains alive at six years end 64,

At sixteen years end  40

At twenty-six             25

At thirty-six               16

At forty-six                10

At fifty-six                   6

At sixty-six                 3

At seventy-six             1

At eighty                      0"

Fortunately, as demographic methodology has improved, I think the idea behind a life table has gotten easier to understand too.  He has a point though.  Men don't die in fractions.  This leads to a phenomenon that can be an issue in small populations known as demographic stochasticity. 

I particularly love the causes of death that Graunt enumerates.  Here are the "notorious diseases": Apoplexy (1,306), Cut of the Stone (38), Falling Sickness (74), Dead in the streets (243), Gowt (134), Head-Ache (51), Jaundice (998), Lethargy (67), Leprosy (6), Lunatick (158), Overlaid, and Starved (529), Palsy (423), Rupture (201), Stone and Strangury (863), Sciatica (5), Sodainly (454).

And here are the "casualties": Bleeding (69), Burt and Scalded (125), Drowned (829), Excessive drinking (2), Frighted (22), Grief (279), Hanged themselves (222), Killed by several accidents (1,021), Murdered (86), Poisoned (14), Smothered (26), Shot (7), Starved (51), Vomiting (136).

Just in case you were still harboring illusions that 17th century London was not a violent place...

Durkheim is typically credited with discovering structure in society.  Seems to me like John Graunt might have a claim to that 200 years before him.  Surely, there is an implied regularity to the means by which death is meted out in Graunt's primitive life table.  Much of Graunt's essay can be found here. The full text can be found in the Journal of the Institute of Actuaries, 1964, volume 90.

On Journal Impact Factors

How do we evaluate the quality of published work?  This has become an issue for me recently for one general and two more specific reasons.  The general reason is that as one approaches one's tenure decision, one tends to think about the impact of one's oeuvre. The specific reasons are, first, I have a paper that I know has been read (and used) by a substantial number of people but was published in a journal (The Journal of Statistical Software) that is not indexed by Thompson Scientific, the keepers of the impact factor. Will this hurt me or any of the other people who write useful and important software (and perform all the research entailed in creating such a product) when I am evaluated on the quality of my work?   The second reason this question has taken on relevance for me is that I am an Associate Editor of PLoS ONE, another journal that is not indexed by Thompson. One of my duties as an AE is to encourage people to submit high-quality papers to PLoS ONE.  This can be tricky when people live and die by a journal's impact factor.

The thing that irks me about Thompson's impact factors is how opaque they are.  Thompson doesn't have to answer to anyone, so they are free to do whatever they want (as long as people continue to consume their products).  Why do some journals get listed and others don't?  What constitutes a "substantive paper" (the denominator for the impact factor calculation)?  What might the possible confounds be?  What about biases? We actually know quite a bit about these last two.  We know very little about the first two.

Moyses Szklo has a nice brief editorial in the journal Epidemiology, describing a paper in that same journal by Miguel Hernán criticizing the use of impact factors in epidemiology.  The points clearly apply to science more generally.  Three key isues affecting a journal's impact factor listed by Szklo are: (1) the frequency of self-citation, (2) the proportion of a journal's articles that are reviews (review papers get cited a lot), and (3) the size of the field being served by the journal.  Hernán's paper is absolutely marvelous.  He notes that the bibliographic impact factor (BIF) is flawed -- as a statistical measure, not by the manipulations described by Szklo -- for three reasons: (1) a bad choice of denominator (total number of papers published), (2) the need to adjust for variables that are known to affect the measure, (3) the questionability of the mean as a summary measure for highly skewed distributions (as we know BIFs have). Hernán makes his case by presenting a parallel case of a fictional epidemiological study. To anyone trained in epidemiological methods, this case is clearly flawed.  It is exactly analogous to the way that Thompson calculates BIFs, yet we continue to use them.  The journal, Epidemiology, also published a number of interesting responses to Hernán's paper criticizing the use of BIFs (Rich Rothenberg, social network epidemiologist-extraordinaire has a nice counterpoint essay to these). The irony is that on the Epidemiology front page, they advertise the journal by touting its impact factor!

The rub, of course, is that formulating a less flawed metric of intellectual impact is clearly a very demanding task.  Michael Jenson, of the National Academies, has written The New Metrics of Scholarly Authority.  One of the key concepts is devising a metric that measures quality at the level of the paper rather than the level of the journal.  We've all seen fundamentally important papers that, for whatever reason, get published in obscure journals.  Similarly, we regularly see the crap that comes out in high-prestige journals like Science, Nature, and PNAS every week!  Pete Binfield, the managing editor of PLoS ONE notes that Jenson's ideas are very difficult to implement.  Pete is leading the way for PLoS to think about alternative metrics like the number of downloads, the number of ping-backs from relevant (uh-oh, more subjectivity!) blogs, number of bookmarks on social bookmark pages, etc.  Another way to handle Thompson's monopoly is to use alternative metrics such as those created by Scopus or Google Scholar.  This last suggestion, while worth pursuing in the spirit of competition, is still not entirely satisfying because to whom in Science do these organizations have to answer?  I am particularly leery of Scopus because it is run by Elsevier, a big for-profit publishing house that also clearly has it's own agenda.  PubMed is, at least, public and for the public benefit.  Of course, they don't index all journals either -- not too many Anthropology journals indexed there!

Björn Brembs, another PLoS ONE AE, makes the very reasonable suggestion that an impact factor should, at the very least, be a multivariate measure (in accordance with the criticism of lack-of-adjustment for confounders in Hernán's essay).  Björn, in another blog posting, cites a paper published last year in PLoS ONE that I have not yet read, but clearly need to.  This paper shows that BIF inconsistently ranks journals in terms of impact (largely because the mean is such a poor measure for citation distributions) and proposes a more consistent measure.  I need to carve some time out of my schedule to read this one carefully.

Some Thoughts on the Fires Down Under

I recently received some comments on my post describing our PNAS paper from the end of 2008 in which we demonstrated that aboriginal burning increases grassland biodiversity.  The comments were very angry -- and a little incoherent.  Clearly, emotions were (and are) running high in Aus following the the tragic bushfires in Victoria that have killed at least 181 people. An interesting, though rather vague, editorial appears in today's The Australian in which foreign editor Greg Sheridan argues it's time to get serious about preventing future tragedies of this kind.  He rightly notes that all the hysteria over global warming is of little practical consequence for managing wildfires. Global warming is, in my opinion, a reality and the best evidence we have suggests it is driven by human action.  Nonetheless, we can not attribute any one event, however dramatic, to global climate change.  Furthermore, blaming the fires on global warming does nothing to mitigate the effects of future fires (which are inevitable both in Aus and here in the American West). If anything, I fear that the linking of these fires to global warming disempowers people for action because they feel like they have no control over forces so much larger than themselves.

One of the comments on Sheridan's editorial really struck me (and I thank Brian Codding for bringing this to my attention).  "Steve from Hobart" wrote quite eloquently on the topic (I have attempted to edit some of the characters that didn't translate from Steve's word processor to The Australian):

The call for controlled burning has long been sounded in this country without being seriously implemented by State and Commonwealth governments of either political persuasion. The Royal Commission after the 1939 fires clearly indicated that such land management practices should be diligently implemented -- long before there were any "greenies". Similar calls came after 1967 in Tasmania, 1983 in SA and Victoria, and more recently in NSW and certainly in Canberra. Conclusion: the inaction on implementation of a systematic, cyclical prescribed burning regime is not new, so be careful about laying the blame on any particular group. Issue 2.: controlled burns a threat to biodiversity??? Perhaps it might be if such burns are only carried out when the fuel load reaches ridiculous proportions, and/or it's allowed to cover very large areas. Controlled burning is something that the ecology and biodiversity of this country thrives on, and it would appear that it has actually evolved to take advantage of a cyclical fire regime. Ask the indigenous people, they practised it for millennia. We need to make a serious effort to revisit that strategy, and not just on the urban fringe. We need to do the ecology and biodiversity of our magnificent and unique country a favour, and try to develop a modern-day fire-stick farming regime for our forests. Regular patchwork burning of smaller areas, repeated on a regular cyclical basis. And, in so doing, we'll protect human life and property.

Well said, Steve!

Here, I will copy what I wrote in response to the heckling I received regarding my previous post because the points are, I think, worth emphasizing. I was responding to extreme skepticism that ecology had anything to do with fire control and that human agency has anything to do with ecology. Again, I will edit slightly.

The tragic fires currently devastating large tracts of Victoria actually highlight the need for carefully done fire ecology. The recent events in Australia dramatically underscore this as do the enormous wildfires that have beset us here in California and the American West more generally over the past decade. So far, we have not experienced the degree of human tragedy that you are seeing in Victoria, but I fear it is just a matter of time.

Following the classic definition by Andrewartha and Birch, ecology is the scientific study of the distribution and abundance of life. If human burning affects either the distribution or abundance of plant or animal species — which it certainly does — then it is the proper subject for ecological analysis. Furthermore, ignoring human agency in such a case would yield a trivial and incomplete ecology.

In our paper on the fire-stick farming hypothesis, we actually make no claims of relevance to contemporary problems. We are trying to understand the dynamics of this particular system. That said, I nonetheless think there are findings of policy relevance embodied in this work. Fire needs fuel and the fuel for wildfires is the vegetation in “wild” areas. As you note, there are no parts of the world untouched by human influence either directly or indirectly. By setting many, small, low-intensity fires through their subsistence hunting, the Martu alter the landscape and make it less flammable. In effect, the successional mosaic that arises from this practice creates a landscape of firebreaks. This is precisely what back-country fire-control teams do in battling wildfires. The Martu just do it preemptively.

How to manage highly flammable landscapes in more densely settled areas like coastal Australia and the American West is an enormous problem and I don’t claim to have the answers. However, ideas informed by landscape ecology are clearly part of the solution. Engineering human-dominated landscapes with greater structural heterogeneity seems essential for dealing with this emerging chronic problem of arid temperate and sub-tropical climates.

Doug Bird, Rebecca Bliege Bird and I are working on longer essay that addresses these vital problems of contemporary human ecology.  I will, no doubt, write about that again here soon.

Always a Bridesmaid, Never a Bride

Well, it's happened again.  My work has been written up in Science but I am not mentioned.  I'm actually not that concerned this time -- we're going to submit the paper for publication soon. I've been telling myself (and other people) that this thing we've ben working on (all the while being very cryptic about what this thing exactly is) is important.  Every once in a while, I wonder if I've just been fooling myself.  The fact that this work has been written up in Science the day after the paper was presented at the Montreal Conference on Retroviruses and Opportunistic Infections suggests to me that it is, indeed, important.

Further Adventures in Publishing

I finally received the pdf version of my recently published paper with a 2006 publication date.  My grad student, Brodie Ferguson, and I used demographic data from the Colombia censuses of 1973, 1985, 1993, and 2002 to calculate the magnitude of the marriage squeeze felt by women in Colombia.  The protracted civil conflict in Colombia means that there has been a burden of excess young male mortality in that country for at least 30 years (the measurement of which is the subject of a paper soon to be submitted).  This excess male mortality means that there are far more women entering the marriage market than there are men, putting the squeeze on women (i.e., making it more difficult for them to marry).  Our results show that in the most violent Colombian departments at the height of the violence (1993), the marital sex ratio was as low at 0.67.  This means for every 100 men entering the marriage market, there were 150 women.  This is a truly stunning number.  We discuss some of the potential societal consequences of these incredibly unbalanced sex ratios.  Two very important phenomena that we think are linked to these extraordinary sex ratios are: (1) the high rates of consensual unions (i.e., non-married couples "living together") in Colombia and (2) the pattern of female-biased rural-urban migration.

The citation to the paper (even though it came out in 2008) is:

Jones, J. H., and B. D. Ferguson. 2006. The Marriage Squeeze in Colombia, 1973-2005: The Role of Excess Male Death. Social Biology. 53 (3-4):140-151.

Adventures in Publication 2003-2008

A couple weeks ago, a colleague wrote me asking for a pdf copy of a paper that I had in press.  I told him that I would be happy to send him the file if I ever got it. You see, the paper had been "in press" since 2006.  When I said this, he informed me that he was looking at the actual journal with my paper in it; he just wanted a pdf copy so he could use it in class.  Since I had heard nothing about the publication and he just happened to be looking at the hard copy, I asked if he would be so kind as to send me the publication information so I could update my CV.  The citation is as follows:

Jones, J. H., and B. D. Ferguson. 2006. The Marriage Squeeze in Colombia, 1973-2005: The Role of Excess Male Death. Social Biology. 53 (3-4):140-151.

2006!  How can a paper published in December of 2008 have a 2006 publication date on it?  Turns out, it's complicated. It seems that the journal Social Biology has been undergoing some substantial changes and has a horrible backlog of papers.  Apparently there was a big debate at the board meeting at last year's PAA meeting about how to deal with this.  The decision was to maintain continuity, which meant publishing papers in order even if the publication date was two years off at the time of publication. Oh well.  I can't decide whether this is a good or bad thing.  2006 was actually a pretty thin year for me in terms of publications (I was busily trying to learn some new skills as part of my career award and this has a way of slowing the mill), so there might actually be a silver lining to this cloud of delayed publication.  I would link to the paper, but I still don't have a pdf!

Another publication that finally came out was a chapter in a book that Melissa Brown edited.  This book publishes the papers given in a conference held in January of 2003 here at Stanford.  This actually happened before I arrived at Stanford (though I already had accepted the job offer) while I was still a post-doc at the University of Washington.

Jones, J.H. 2008. Culture for epidemic models and epidemic models for culture. In M. Brown, ed., Explaining Culture Scientifically, Seattle: University of Washington Press. pp. 117-136.

Wow, books take a long time to get published.  It was weird when I got the proofs for this chapter earlier this year.  I hadn't thought about the material in this chapter, literally, in years.  I'm back thinking about this stuff again, albeit in a slightly different form.  But that's material for another post...