PDF《Beyond Black Box Epidemiology》

7 it is not clear how that integra- tion can occur. An examination of the nature of black boxes, black box thinking, and their parent concept, systems theory, provides a clue. Black Box Epidemiology One first needs to take a black box to be a metaphor for the individual organism and take black box tinking to be a method- ology that ignores rather than explores the insides ofthe box. One then places the black box near the middle of a structure of scien- tific knowledge that has recently been labeled as a set ofChinese boxes-each one nested inside another.'

0 There, the environ- ment, interpersonal dynamics, and social forces such as race, ethnicity, economics, and politics lie above the level ofthe indi- vidual, while organ systems, cells, genes, proteins, atoms, and quarks lie below that same level.'

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23 Black box thinking labels the methodologic approach that ignores biology and thus treats all levels of the structure below that of the individual as one large opaque box not to be opened. For some,7 black box hinking is inde- fensible-hence, the pejorative connota- tion. A serious problem with such an opin- ion, however, is that the same negative labeling can apply to scientists who ignore other parts of the structure. After all, unopened black boxes lie above and below every level. Thus, black box thinking labels molecular biologists who fail to explain DNA repair in terms of quantum forces or other entities below molecules. It also characterizes molecular epidemiologists who fail to examine the behavioral implica- tions ofgenetic knowledge. An unfortunate legacy of the first his- torical thread, therefore, is a pejorative label for epidemiologists who constrain their conceptualization of the proper domain of investigation. To reach the more expansive view found in the second historical thread, a constructive change in the way we use the ideas ofblack boxes and black box thinking is necessary. This change represents more than a new set oflabels;

it is a change in the way epidemiologists view what is impor- tant in disease etiology and prevention, a change in conceptual framework. It is called a general systems approach and iron- ically, a black box is neither a limiting construct nor a derogatory label. Rather, it is a central precept. A simple system is composed of inputs, outputs, and mathematical model(s) in between.'

4 A 2-by-2 table, the essence of epidemiological analysis, is a simple sys- tem, with the input to the black box being the counts of diseased and nondiseased classified by exposure status, the output being the relative risk estimate, and the model being a formula for the odds ratio. Employment selection and its impact on health status-the healthy worker effect -is another example,'

5 as are infec- tious disease transmission processes'

6 and population screening programs.'

7 Engineers have developed systems analysis most extensively, and they teach that a complete understanding of the inner components of a black box at any level of inquiry is impossible.'

8 All mathematical models are imperfect representations of reality, although a good model of the inner components is preferred if controlling out- put is the goal. A central premise of sys- tems theory is that the knowledge of the box'

s interior and control ofits input-output relationships are closely linked. A wide variety of models, including nonlinear, lin- ear, static, or dynamic, are possible;

the best model is one that best represents input- output measurements. More complex systems arise when the size and scope of the mathematical model are increased (e.g., through parameteriza- tion) and black boxes are linked together- that is, when the mathematical models developed within the boxes are linked together. The input to one box can represent the output from another. Indeed, when faced with a problem as complex as that represented by the broad structure of scien- tific knowledge described earlier, a systems analyst will use a divide and conquer strategy in which subsystems-the black boxes at each level of the structure-are investigated separately and independently, followed by a more detailed characteriza- tion of their connections (K. Lilly Jablokow, personal communication). Even this incomplete presentation of the principles and practice of systems the- ory warrants the conclusion that the approach has merit. I believe epidemiolo- gists should embrace rather than denigrate the idea ofblack boxes. BeyondBlack Boxes Despite its many strengtis, a systems approach also has weaknesses, especially when a good mathematical model is not available at a particular level of explana- tion.'