Do socioeconomic characteristics modify the short term association between air pollution and mortality? Evidence from a zonal time series in Hamilton, Canada.

STUDY OBJECTIVE: To assess the short term association between air pollution and mortality in different zones of an industrial city. An intra-urban study design is used to test the hypothesis that socioeconomic characteristics modify the acute health effects of ambient air pollution exposure. DESIGN: The City of Hamilton, Canada, was divided into five zones based on proximity to fixed site air pollution monitors. Within each zone, daily counts of non-trauma mortality and air pollution estimates were combined. Generalised linear models (GLMs) were used to test mortality associations with sulphur dioxide (SO(2)) and with particulate air pollution measured by the coefficient of haze (CoH). MAIN RESULTS: Increased mortality was associated with air pollution exposure in a citywide model and in intra-urban zones with lower socioeconomic characteristics. Low educational attainment and high manufacturing employment in the zones significantly and positively modified the acute mortality effects of air pollution exposure. DISCUSSION: Three possible explanations are proposed for the observed effect modification by education and manufacturing: (1) those in manufacturing receive higher workplace exposures that combine with ambient exposures to produce larger health effects; (2) persons with lower education are less mobile and experience less exposure measurement error, which reduces bias toward the null; or (3) manufacturing and education proxy for many social variables representing material deprivation, and poor material conditions increase susceptibility to health risks from air pollution.

Implicit and explicit dialogue structuring in virtual learning groups.

BACKGROUND: The promotion of virtual learning groups by instructional means is gaining importance with the spread of telematic learning. In virtual learning groups, students discuss certain learning materials or cooperate in problem solving by means of computer-mediated communication. Due to the specific features of electronic communication, supportive means appear to be necessary for such learning situations. AIMS: The investigation focuses on testing two different forms of dialogue structuring in virtual learning groups, in which students discuss a given subject matter together and clarify problems in understanding by means of synchronous computer-mediated communication. SAMPLE: Forty-five students from various disciplines at the University of Tübingen, except students of physics, participated in the investigation. METHOD: An experiment was conducted involving three-person groups in a telematic setting with two different kinds of dialogue structuring: implicit structuring induced group discussion on the subject matter by working on key questions in a preceding learning phase, whilst explicit structuring provided additional rules for discussion. These rules prompted group members to argue and aimed at directing them to equal participation. RESULTS: Compared to a control group, both implicit and explicit structuring showed greater orientation on the subject matter and showed less off-task talk. Moreover, explicit structuring led to more coherence in subject matter discussion with regard to the completion of topics. However, post-test performance showed no significant difference in knowledge over that of the control group. CONCLUSION: The results of the investigation show that dialogue structuring can be an adequate pedagogical approach for virtual learning groups.