Tuesday, June 26, 2007

Spit and Blood

...and Other Bodily Fluids We Want from You
While Aco and Anna were being amused in Japan, my middle finger was being pricked for blood by a research psychiatrist whose main field of research include depression and social dysfunction...
We often say that economists are not too interested in learning what people say or what people feel. We are more interested in observing what choices people actually made - revealed preference is an example of this approach. How much then, do you think, one should value the answer to the question "Are you very happy, pretty happy, or not very happy" in surveys? Not very much, if you're an economist. You'd want to be able to observe things that show people really are happy, some objective measures.*)

The similar is true when we want to study health status of individuals. Self-reported measures of health status (e.g. "How would you rate your overall health?"), while valuable, are subjective, prone to error, and often misreported. So we would look for "hard" evidence in the form of objective health measures to complement the self-reported measures. Robert Fogel, in one of his famous studies, look at long-term trend in height of individuals to study health, nutrition, and economic growth. There is now a large literature in economics that utilizes anthropometric data such as height and weight in various forms (Body Mass Index, weight-for-height Z-scores, waist circumference, etc.).

In recent years, economists as well as other social scientists have looked at other sources of "hard evidence": saliva, blood drops, urine, and practically any other bodily fluids they can have their hands on. These are of course some of the things that people in biology, medicine, and epidemiology have been studying in their respective fields. But several development have transformed activities that previously could only be conducted in a laboratory setting in such ways that they can now be done in the context of large scale population-based research.

First, the cost of doing so has never been cheaper. Equipment to measure blood pressure, blood hemoglobin level, cholesterol levels, are becoming smaller and cheaper. Methods to analyze blood sample from a dried drop of blood have been developed - no need to collect a whole tube- enabling researchers to incorporate blood sample collection into their large scale surveys. Second, researchers are realizing that so long as they follow strict ethical guidelines, people are willing to provide blood, urine, or saliva.**) In contrast, people are more guarded about their earnings, savings, or wealth. And this is true not only in developing countries but also in developed countries: people are generally more willing to spit for you than they are in telling you how much money they make last year.

, scientists have been able identify some biomarkers that can be linked to various health and behavioral outcomes. For example, the level of cortisol, a hormone that is released by our body in response to stress, could be useful for those who are interested in learning how negative events influence one's health. Asking "Are you stressed out?" could be useful too, but having objective measure as well would certainly be better. We can obtain cortisol levels by analyzing saliva (preferably collected at different times of day, because of its diurnal variation). C-reactive protein, a protein that is released during inflammatory episodes can be measured from a small spot of dried blood. There is now a body of evidence linking C-reactive protein levels with elevated risk of hypertension, cardiovascular disease, and diabetes. In this Cafe a while ago, Aco mentioned an economic paper that looks at cotinine level in blood. By collecting these objective measures of health, social scientists now have better access to study the relationship between health and socioeconomic status and the two-way nature of the relationship.

So there I was, my middle finger being pricked for blood by this research psychiatrist whose main field of research include depression and social dysfunction..

We were both eager participants of a workshop designed to equip social scientists with tools on how to integrate biomarkers into our research. There were psychiatrists, psychologists, demographers, sociologists, economists, and anthropologists in the room (note: some biological anthropologists are at the frontier of this interdisciplinary research) .

Part of the fun -besides exchanging bodily fluids- is to learn about the new terminologies and compare them to things we have in our own discipline. Take homeostasis, for example, the property of our bodies to internally maintain a stable condition regardless of changes in outside environment. Example: our body has a "thermostat" that regulates internal temperature that keeps our body from becoming too hot - we sweat. Economists would perhaps associate homeostasis with a steady state equilibrium. And there's allostasis, the process of maintaining stability or homeostasis through changes in physiological or behavior. Example: having endured prolonged exposure to heat, we will not only be sweating, but our kidneys will start to reduce urine output, eyes begin to dry out and so forth. Economists: think of allostasis is the process of moving from an old to a new equilibrium level, if there are multiple equilibria. And the fun goes on.

A look back at older posts and comments in this Cafe would reveal that many of the Cafe's visitors (Tirta, Roby, just to name a few) are already well-versed in inter-disciplinary crossovers. I, dear readers, still have a lot to learn.

*) There is of course a strand of literature in economics that increasingly take subjective measures of well-being seriously. See, for example, the paper by Kahnenman and Krueger in the Journal of Economic Perspectives, 2006 (20:1) on the topic. And yes, I know about Bhutan's Gross National Happiness project.
**) The ethical part of this body of research is something that cannot be taken for granted. Just last week, there was an article in the New York Times about a group of Amazon Indians who were aggrieved when they found out (from the internet!) that blood samples that were collected from them years ago are now being sold to researchers around the world.

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