Demography and epidemiology: past and future directions

Epidemiology and demography are often so close that it can be difficult to distinguish one from the other. Is it necessary to train health demographers when epidemiologists could just as well do the job? Could researchers from either field learn something from each other? As my first post for Demotrends, I thought I’d share some of my initial thoughts.

The reasons for the similarities between the two fields, and the reason why early demographers like John Graunt, were also public health experts, are not surprising. Demographers are interested in the size and structure of populations, and the force of mortality is one of the three primary mechanisms that affect size and structure. The fact that mortality is primarily affected by population health therefore resulted in demography and epidemiology becoming bedfellows.

This also defines the difference between the two disciplines. Epidemiologists are less interested in population in itself and more in the diseases that affect individuals. It is more focused on the ‘micro-level’ (the level of individuals), whereas demographers are more interested in the ‘macro-level’ (the aggregate level). At least, that was one of the cases made here. My initial observation is that this is largely true; most of my epidemiologist colleagues are pharmacists, bio-medical scientists or medical doctors first, and epidemiologists second. They will engage a problem at the micro level, and afterwards perhaps generalize to the macro level; whereas demographers are more prone to work the other way around. This different approach may also lead us to different conclusions and recommendations. Therefore, despite the strong similarities and common roots, there are also many small differences, resulting in synergy when the two fields are combined.

PharepiDemo

Pharmacoepidemiologists and Demographers can learn a lot from each other.

For the more adventurous demographers with health interests, there are some promising new subfields in which we can immerse ourselves. My primary interest is in the combination of pharmacoepidemiology and demography. Pharmacoepidemiology, the study of prescription drug use and its consequences in populations, is a fairly new discipline and therefore quite untouched by demographers, yet advances in drug research can have a profound impact on populations and therefore deserves our attention. To give some other (perhaps better) examples of the future directions of demography and health, I expect to see some very interesting results from biodemographic research (e.g. that of the Max Planck Institute for Demographic Research). This research puts human ageing and mortality in the context of biological ageing and the mortality of animals in general. One finding may be that humans are not so different from (other) animals, meaning we will be able to answer important questions on disease progression and mortality through the proxy of animal research. Alternatively, we will find the ways in which we differ from other species (which is informative in its own right). A final example that should be mentioned is that demographers are also becoming more involved in genetics (though this is not limited to ageing and mortality; we hope to a have a post on the topic of genetics and fertility in the near future from an investigator specialising in this). Insight from this field may radically alter current theories on human behaviour, which still tend to be more social rather than biologically informed.

It is quite likely that I missed some promising new subfields of demography, so I would love to know what you think worth the attention of the community of demographers. Comments or questions are also much appreciated!

7 comments

  1. Thanks for reblogging @sarahphillipsmph!

  2. Philipp · · Reply

    There was actually a forum on this topic at the last PAA. To be honest Samuel Preston presented a very static picture of demography as a discipline: population=country; all that demographers care about=mean & aggregate statistics

    Epidemiology sounded much more modern: caring about risks, heterogeneity, effect sizes, endogeneity (aka confounding), actual diseases and their etiology

    if I had heard this earlier, I guess I wouldn’t have studied demography 😉

  3. Thanks for your comment @Philipp! Of course I exaggerate a bit when I say the two disciplines are ‘almost the same’ ;).

    One of the reasons why I chose to combine demography with pharmacoepidemiology is because the latter spices up the ‘traditional’ demography a bit because demography on its own can appear (emphasis on appear) to be somewhat static. However, in practice I don’t think demography is static at all. Demographic techniques are still being refined and demographic trends, as you know, are changing (e.g. demographic transition, new diseases and environmental challenges ahead).

    Epidemiology is probably changing faster, though but in the end, the big developments are going to be interdisciplinary. Demography is sometimes referred to as an ‘interdiscipline’, so I don’t think you should regret your choice ;). At least, if you dare to wander into other disciplines a bit ;P.

  4. Basically demography studies the change of the population in terms of its size, influenced by fertility, mortality and migration. The correspondence to that in the field of health is not epidemiology but “public health”, which looks at the change in health status at the population level. Of course many demographers and public health scientists do also perform studes at the micro level (e.g. using epidemiological methods!) but I believe that the study of the whole population is their unique selling point in the whole health business. What makes a population sick (e.g. too much use of antiobiotics) could be fundamentally different from what makes an individual sick (to little use of anibiotics). As many practioners (as for instances MDs) are trapped in their focus on persons in their daily work, the counterintuitive system-level thinking – which is natural for demographers – could add a lot to many fields in health and elsewhere. A classical paper that clearly illustrated this point is the Vaupel/Yashin 1985 about the impact of heterogeneity on the survival of a cohort of people, where the authors show that the population-level survival could be completely different from the “real” survival of its sub-cohorts: http://www.jstor.org/discover/10.2307/2683925?uid=3737864&uid=2&uid=4&sid=21104132602073

  5. Thank you for your useful comment on macro vs micro thinking, Fred!

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