Quantifying uncertainty in the biospheric carbon flux for England and Wales

Summary.  A crucial issue in the current global warming debate is the effect of vegetation and soils on carbon dioxide (CO₂) concentrations in the atmosphere. Vegetation can extract CO₂ through photosynthesis, but respiration, decay of soil organic matter and disturbance effects such as fire return it to the atmosphere. The balance of these processes is the net carbon flux. To estimate the biospheric carbon flux for England and Wales, we address the statistical problem of inference for the sum of multiple outputs from a complex deterministic computer code whose input parameters are uncertain. The code is a process model which simulates the carbon dynamics of vegetation and soils, including the amount of carbon that is stored as a result of photosynthesis and the amount that is returned to the atmosphere through respiration. The aggregation of outputs corresponding to multiple sites and types of vegetation in a region gives an estimate of the total carbon flux for that region over a period of time. Expert prior opinions are elicited for marginal uncertainty about the relevant input parameters and for correlations of inputs between sites. A Gaussian process model is used to build emulators of the multiple code outputs and Bayesian uncertainty analysis is then used to propagate uncertainty in the input parameters through to uncertainty on the aggregated output. Numerical results are presented for England and Wales in the year 2000. It is estimated that vegetation and soils in England and Wales constituted a net sink of 7.55 Mt C (1 Mt C = 10¹² g of carbon) in 2000, with standard deviation 0.56 Mt C resulting from the sources of uncertainty that are considered.     

Dose-Response and Risk Assessment of Airborne Hexavalent Chromium and Lung Cancer Mortality

This study evaluates the dose-response relationship for inhalation exposure to hexavalent chromium [Cr(VI)] and lung cancer mortality for workers of a chromate production facility, and provides estimates of the carcinogenic potency. The data were analyzed using relative risk and additive risk dose-response models implemented with both Poisson and Cox regression. Potential confounding by birth cohort and smoking prevalence were also assessed. Lifetime cumulative exposure and highest monthly exposure were the dose metrics evaluated. The estimated lifetime additional risk of lung cancer mortality associated with 45 years of occupational exposure to 1 microg/m3 Cr(VI) (occupational exposure unit risk) was 0.00205 (90%CI: 0.00134, 0.00291) for the relative risk model and 0.00216 (90%CI: 0.00143, 0.00302) for the additive risk model assuming a linear dose response for cumulative exposure with a five-year lag. Extrapolating these findings to a continuous (e.g., environmental) exposure scenario yielded an environmental unit risk of 0.00978 (90%CI: 0.00640, 0.0138) for the relative risk model [e.g., a cancer slope factor of 34 (mg/kg-day)-1] and 0.0125 (90%CI: 0.00833, 0.0175) for the additive risk model. The relative risk model is preferred because it is more consistent with the expected trend for lung cancer risk with age. Based on statistical tests for exposure-related trend, there was no statistically significant increased lung cancer risk below lifetime cumulative occupational exposures of 1.0 mg-yr/m3, and no excess risk for workers whose highest average monthly exposure did not exceed the current Permissible Exposure Limit (52 microg/m3). It is acknowledged that this study had limited power to detect increases at these low exposure levels. These cancer potency estimates are comparable to those developed by U.S. regulatory agencies and should be useful for assessing the potential cancer hazard associated with inhaled Cr(VI).     

TEACHING TOOLS: ON JOURNALISTS' USE OF MACROECONOMIC CONCEPTS

Five macroeconomic concepts are presented which are prominent in the business sections of newspapers, but which are not given equivalent prominence in macroeconomic textbooks. These are the discouraged worker phenomenon, the use of inventories in forecasting, the effect of changes in the money supply on the bond market, and the effects of inflation and nominal interest rates in the foreign exchange market. These concepts are presented via news clips illustrating the way they typically appear in the press. Instructors are urged to place extra emphasis on these concepts.     

Getting the most for your consulting dollars

Major changes in the health care financing and delivery system have usually been accompanied by an increase in demand within the health care field for consulting services. The passage of Medicare/Medicaid in 1965 is one example. The passage of the DRG-based prospective pricing system in 1983 is another. Both spawned a substantial amount of work, and income, for consulting firms. Now the health care field is engaged in nearly total transformation as the forces of health care reform at the national level are met with myriad adjustments at the local and regional levels. Managed care, already a byword, is being strengthened by a multitude of so-called integrated system initiatives. It is not easy to survive, and the call is out to consultants to save the day, or at least stave off disaster. In the following four articles, Marilyn Kennedy, a member of the ACPE faculty and a consultant herself, gives some advice on how to make the consulting arrangement successful; three physician executives provide a glimpse at consults that have worked, and some that did not work.     

Personal trainer, personal coach

The increasing number of fresh faces in the management ranks, many of them with highly polished credentials but little in the way of practical experience in the work-a-day management world, has increased the need for a new consulting professional--the personal coach. There simply aren't enough volunteer mentors to accommodate the growing medical management profession. Whatever the conditions under which this new professional's services are sought, both the individual to be coached and the organization for which the individual works should approach the arrangement with care and planning. The author offers some guidance for making the arrangement pay off.     

Can you communicate cross-generationally?

What is fractured cross-generational communication? When what one person heard was not what the other person said. Regardless of your age, you need to understand some of the differences in communication styles that must be overcome if people are to work well together. This is especially important in health care right now when there are other pressing issues. Interpreters are at a premium because so much misunderstanding clouds the communication process. Two management strategies are presented that will help bridge the gaps between communication styles.     

How could I have gotten it wrong?

Can you avoid ending up in a career-denting job: Are there potential pitfalls to recognize on the search for a rewarding position? Finding oneself in an impossible job, working for a boss who brings out your worst qualities and deepest insecurities, or joining an organization that is doomed are nightmare scenarios. How do these judgment errors happen? We asked physicians who've been there and, unfortunately, done just that. What they learned might help the rest of us skip the experience.     

Cognitive distortions predict future gambling involvement

Disordered gambling is best conceptualized as a continuum of severity. Previous research has demonstrated the utility of studying individuals at all points of this spectrum. The sequence of the development of gambling problems and change in gambling involvement along this continuum of severity is not well understood. The present study examined the interplay between cognitive distortions and gambling involvement in a population sample recruited in Alberta, Canada. Data from 1372 participants over 4 assessment waves (5 years) were used to generate a 2-factor latent structure using gambling fallacies and gambling involvement measurements. Structural equation modelling showed that cognitive distortions more strongly predicted future gambling involvement than the reverse relationship, using the comparative fit index (CFI) and the root mean square error of approximation (RMSEA) to assess the models. In addition, cognitive distortions declined over time, whereas gambling involvement remained stable. The results of the study suggest that focusing primarily on cognitive mechanisms in public health initiatives for gambling disorders may be a more effective strategy than focusing on behavioural solutions.