Center for Interdisciplinary Research
in Environmental Exposures and Health
Main / Spatial Epidemiology at Boston University School of Public Health

The Spatial Epidemiology Group at Boston University School of Public Health has several interests:

  • disease mapping and clusters
  • time-space analysis
  • ecologic bias
  • the use of combinations of individual- and group-level data (multi-level studies)
  • the use of Geographic Information Systems (GIS) in exposure assessment

Disease Mapping and Clusters
Disease registry data are often mapped by town or county of diagnosis and contain limited data on possible confounders. These maps often possess poor spatial resolution, the potential for spatial confounding, and the inability to consider latency. Population-based case-control studies can, on the other hand, provide detailed information on residential history and covariates. We are developing and applying methods for mapping case-control and cohort data while adjusting for risk factors and latency. We map point patterns using generalized additive models (GAMs), a statistical framework which allows us to analyze binary outcome data, adjust for covariates, smooth on space (with optimal degree of smoothing), and perform hypothesis tests. For example, the map on the left above shows breast cancer risk at the time of diagnosis; the map on the right shows maps residential location twenty years prior to diagnosis. We are also working on time-space clustering.

Ecologic bias
Individual-level studies collect information on exposure, outcome and covariates for each individual; purely ecologic studies collect group-level (aggregate) information for these variables. Ecologic bias can occur when aggregate data are used to make inferences about individuals. We are interested in comparing the direction and magnitude of ecologic bias compared with biases occuring on the individual-level. Such information is useful in designing ecologic studies, doing sensitivity analyses of ecologic studies, and understanding what happens when a group-level variable is used in an otherwise individual-level study (e.g., as a proxy for exposure on the individual-level). For more information, look here.

Multi-level studies
Many diseases are associated with an individual's socioeconomic status (SES), also known as socioeconomic position (SEP). Community level SES is often associated with disease risk as well. However, despite our knowledge of these separate associations, most previous research has not examined individual and community SES simultaneously. As a result, it is unclear if the greater disease incidence in certain communities is related to the SES of the individuals who live there (composition) or because some aspect of living in a the community confers a greater risk of disease, regardless of their SES (context). A recent paper investigated this question for breast cancer on Cape Cod.

News & Awards (For details, look here)

  • September 2011: A series of four papers on the power and type I error rates of our mapping approach (using gams) have now been published--see papers below with first author Bliss/Young.
  • 28 August 2010: We ran a half day workshop on Disease Mapping using Generalized Additive Models at ISES/ISEE 2010.
  • 19 July 2010: Two new papers examine the statistical properties of using GAMs for mapping of disease. GAMs compare favorably with the widely used spatial scan statistic SaTScan in many cases.
  • 26 March 2010: Graduate student Robin Young defends her dissertation "Properties of Hypothesis Tests Using Generalized Additive Models with Smoothers of Geographic Location in Spatial Statistics"
  • 25 March 2010: New paper on the spatial distribution of rheumatoid arthrititis in the US.
  • 13 October 2008: Our recent time-space analysis of breast cancer was covered in the Cape Cod Times.
  • 22 September 2008: Our multilevel analysis of breast cancer was featured in a National Institute of Environmental Health Sciences (NIEHS) press release on spatial epidemiology.
  • 13 August 2008: New publication on time-space clustering of breast cancer on Cape Cod, including a cool animation, Vieira et al 2008.
  • 25 April 2008: New publication on multilevel modeling of breast cancer and socioeconomic status on Cape Cod, Webster et al 2008.
  • Workshop on ecologic inference: 28-30 November 2007, DIMACS, Rutgers University
    The workshop is part of the DIMACS Special Focus on Computational and Mathematical Epidemiology. The focus will be on study designs combining individual and group level data. More information on the workshop
  • 5 July 2007: New publication. Webster TF. Bias magnification in ecologic studies: a methodological investigation. Environmental Health 2007; 6:17. The full text is freely available here.

Recent publications:

  • Bliss RL, Weinberg J, Vieira VM, Webster TF. Adjusted significance cutoffs for hypothesis tests applied with generalized additive models with bivariate smoothers. Spatial and Spatio-temporal Epidemiology [accepted]
  • Gallagher LG, Vieira VM, Ozonoff DM, Webster TF and Aschengrau A. Risk of breast cancer following exposure to tetrachloroethylene-contaminated drinking water in Cape Cod, Massachusetts: reanalysis of a case-control study using a modified exposure assessment. Environmental Health 2011, 10:47 [21 May 2011]. doi:10.1186/1476-069X-10-47.
  • Bliss RY, Weinberg J, Vieira VM, Ozonoff A, Webster TF. Power of Permutation Tests Using Generalized Additive Models with Bivariate Smoothers. J Biomet Biostat 2010; 1:104. [Online 11 November 2010]. The full text is freely available doi:10.4172/2155-6180.1000104.
  • Young RL, Weinberg J, Vieira V, Ozonoff A, Webster TF. A power comparison of generalized additive models and the spatial scan statistic in a case-control setting. International Journal of Health Geographics 2010, 9:37. [Online 19 July 2010]. The full text is freely available doi:10.1186/1476-072X-9-37
  • Young RL, Weinberg J, Vieira VM, Aschengrau A, Webster TF. A multilevel non-hierarchical study of birth weight and socioeconomic status. International Journal of Health Geographics 2010, 9:36 [Online 9 July 2010]. The full text is freely available doi:10.1186/1476-072X-9-36.
  • Young RL, Weinberg J, Ozonoff A, Vieira V, Webster TF. Generalized Additive Models and Inflated Type I Error Rates of Smoother Significance Tests. Computational Statistics & Data Analysis 2011; 55:366-374. doi:10.1016/j.csda.2010.05.004.
  • Vieira VM, Hart JE, Webster TF, Weinberg J, Puett R, Laden F, Costenbader KH, Karlson EW. Association between Residences in U.S. Northern Latitudes and Rheumatoid Arthritis: A Spatial Analysis of the Nurses’ Health Study. Environ Health Perspect. 2010; 957–961 [Online 25 March 2010]. The full text is freely available doi:10.1289/ehp.0901861.
  • Gallagher LG, Webster TF, Aschengrau A, Vieira VM. Using Residential History and Groundwater Modeling to Examine Drinking Water Exposure and Breast Cancer. Environ Health Perspect. 2010; 118(6):118:749–755 [Online 17 February 2010]. The full text is freely available doi:10.1289/ehp.0901547.
  • Hoffman K, Webster TF, Weinberg JM, Aschengrau A, Janulewicz PA, White RF, Vieira VM. Spatial analysis of learning and developmental disorders in upper Cape Cod, Massachusetts using generalized additive models. International Journal of Health Geographics 2010, 9:7. The full text is freely available doi:10.1186/1476-072X-9-7.
  • Vieira VM, Webster TF, Weinberg J, Aschengrau A. Spatial analysis of bladder, kidney, and pancreatic cancer on upper Cape Cod: An application of generalized additive models to case-control data. Environmental Health; 2009, 8:3. [Online 10 February 2009]. The full text is freely available doi: 10.1186/1476-069X-8-3
  • Vieira VM, Webster TF, Weinberg JM, Aschengrau A. Spatial-temporal analysis of breast cancer on Upper Cape Cod, Massachusetts. International Journal of Health Geographics 2008, 7:46. The full text is freely available here.
  • Webster TF, Hoffman K, Weinberg J, Vieira V, Aschengrau A. Community and Individual-Level Socioeconomic Status and Breast Cancer Risk: Multi-level Modeling on Cape Cod, MA. Environ Health Perspect 2008; 116(8):1125-1129. doi:10.1289/ehp.10818. [Online 25 April 2008]. The full text is freely available here.
  • Webster TF. Bias magnification in ecologic studies: a methodological investigation. Environmental Health 2007; 6:17 (5 July 2007). The full text is freely available here.
  • Webster T, Vieira V; Weinberg J; Aschengrau A. Method for mapping population-based case-control studies using Generalized Additive Models. International Journal of Health Geographics 2006, 5:26 (9 June 2006).The full text is freely available here.
  • Ozonoff A, Webster T, Vieira V, Weinberg J, Ozonoff D, Aschengrau A. Cluster detection methods applied to the Upper Cape Cod cancer data. Environmental Health: A Global Access Science Source 2005, 4:19 (15 September 2005). The full text is freely available here
  • Vieira V, Webster T, Weinberg J, Aschengrau A, Ozonoff D. Spatial analysis of lung, colorectal, and breast cancer on Cape Cod: An application of generalized additive models to case-control data. Environmental Health: A Global Access Science Source 2005, 4:11 (14 June 2005). The full text is freely available here.
  • Webster, T. Commentary: Does the spectre of ecologic bias haunt epidemiology? International Journal of Epidemiology 2002; 31:161-162. The full text is freely available here.

Recent conference presentations:

  • Vieira V, Gallagher L, Ozonoff D, Webster T, Aschengrau A. US. BREAST CANCER RISK AND TETRACHLOROETHYLENE-CONTAMINATED DRINKING WATER IN CAPE COD, MASSACHUSETTS: A REANALYSIS OF CASECONTROL DATA USING GIS, RESIDENTIAL HISTORIES, AND A MODIFIED EXPOSURE ASSESSMENT. International Society for Environmental Epidemiology (Barcelona Spain, 13-16 September 2011).
  • Vieira et al. Spatial analysis of preterm birth risk in Massachusetts to investigate social and environmental risk factors. ISES-ISEE 2010: 2010 Joint Conference of International Society of Exposure Science & International Society for Environmental Epidemiology (Seoul, South Korea, 28 August - 1 September, 2010).
  • Young R, Weinberg J, Vieira V, Webster TF. Geographic Clustering of Disease: Comparison of the Statistical Power of GAMs and SaTScan. ISES-ISEE 2010: 2010 Joint Conference of International Society of Exposure Science & International Society for Environmental Epidemiology (Seoul, South Korea, 28 August - 1 September, 2010).
  • Vieira V, Webster T, Weinberg J, Hart J, Laden F, Costenbader K, Karlson E. Spatial Analysis of Rheumatoid Arthritis in the Nurses' Health Study. Presented at ISEE 2009. Dublin, Ireland, 26-29 August 2009.
  • Young RL, Weinberg J, Vieira V, Webster TF. A Power Comparison of Generalized Additive Models and the Spatial Scan Statistic Under Simple Alternative Hypotheses. Presented at the Joint Statistical Meetings (JSM) 2009 (Washington DC, 1-6 August 2009).
  • Young RL, Weinberg J, Ozonoff A, Vieira V, Webster TF. Generalized Additive Models and Inflated Type I Error Rates of Smoother Hypothesis Tests. Western North American Region of the International Biometric Society (WNAR). Portland OR, 16 June 2009.
  • Webster TF, Vieira VM, Weinberg J, Aschengrau A. Ecologic Measures of Exposure: Can They Cause Ecologic Bias? Presented at ISEE-ISEA 2008 (Pasadena, CA, 12-16 October 2008)
  • Vieira V, Fraser A, Webster T, Howard GJ, Bartell S. Accuracy of Automated and E911 Geocoding Methods for Rural Addresses. Presented at ISEE-ISEA 2008 (Pasadena, CA, 12-16 October 2008)
  • Vieira V, Webster T, Weinberg J, Aschengrau A. Spatial Analysis of Kidney, Pancreatic, and Bladder Cancer on Upper Cape Cod using Generalized Additive Modeling. Presented at ISEE-ISEA 2008 (Pasadena, CA, 12-16 October 2008)
  • Gallagher L, Ozonoff D, Webster T, Vieira V, Weinberg J, Aschengrau A. Reanalysis of the Risk of Breast Cancer and Tetrachloroethylene-Contaminated Drinking Water in Cape Cod, Massachusetts Using a Modified Exposure Assessment. Presented at ISEE-ISEA 2008 (Pasadena, CA, 12-16 October 2008)
  • Vieira V, Webster T, Weinberg J, Aschengrau A. Spatial-temporal analysis of breast cancer as a function of residential history. 2008 Meeting of the Association of American Geographers. 16 April 2008. Boston. MA. AAG 2008
  • Webster, T. Individual studies with ecologic exposure measures. Environmental Statistics Seminar, Harvard School of Public Health. 7 December 2007.
  • Webster, T. Overview: Studies that combine individual and group-level data. DIMACS Workshop on Ecologic Inference. 28 - 30, November 2007, Rutgers University. more information
  • Webster, T. Individual studies with ecologic measures of exposure. DIMACS Workshop on Ecologic Inference. 28 - 30, November 2007, Rutgers University. more information
  • Webster T,Hoffman K, Weinberg J, Vieira V, Aschengrau A. Community and Individual-level Socioeconomic Status and Breast Cancer Risk: Multi-level Modeling on Cape Cod, MA. Society for Epidemiologic Research. Boston, 19-22 June 2007. American Journal of Epidemiology 2007; 165(11) Suppl: S145.
  • Webster T, Weinberg J, Vieira V, Hoffman K, Aschengrau A. The impact of community and individual-level socioeconomic status on the risk of breast cancer: Multi-level modeling in Massachusetts. Presented at ISEE/ISEA, 2-6 September 2006, Paris, France. Epidemiology 2006; 17(6) Suppl:S210
  • Gallagher L, Ozonoff D, Webster T, Vieira V, Aschengrau A. Use of a water distribution model to assess exposure to tetachloroethylene-contaminated drinking water. Presented at ISEE/ISEA, 2-6 September 2006, Paris, France. Epidemiology 2006; 17(6) Suppl:S470-S471.
  • Vieira V, Webster T, Weinberg J, Aschengrau A. Temporal-spatial analysis of breast cancer risk on upper Cape Cod, Massachusetts, USA. Presented at ISEE/ISEA, 2-6 September 2006, Paris, France. Epidemiology 2006; 17(6) Suppl:S484
  • Webster T, Weinberg J, Vieira V, Hoffman K, Aschengrau A. The Impact of Community and Individual-Level Socioeconomic Status on the Risk of Breast Cancer: Multi-level Modeling among Residents of Cape Cod, MA (USA). Presented at Spatial Epidemiology 2006, London.
  • Webster T. Cross-level bias in partially ecologic studies. Presented at Spatial Epidemiology 2006, London.
  • Vieira V, Webster T, Weinberg J, Aschengrau A. Temporal-Spatial Analysis of Breast Cancer on Upper Cape Cod, Massachusetts. Presented at Spatial Epidemiology 2006, London.

Upcoming conferences

Recent conferences

How do we make these maps?
We subscribe to the philosophy of the BU Superfund Research Program (BUSRP) to which we are also connected, i.e., making results and products freely available where possible through open-access publications and open source software available under general public license. We are currently creating maps using S-Plus (to calculate surfaces using GAMs) and ArcView (for mapping the surfaces). R may provide a useful alternative for gams. Our code is freely available, as is some synthetic data for trying it out: here. See also our BUSRP research translation core.

View a movie of breast cancer time-space analysis
The movie shows the risk of breast cancer diagnosis 1983-1993 based on residential history on upper Cape Cod discussed in our new publication, Vieira et al 2008. The movie is a Windows Media file (1 mb). Click to view

Spatial Epidemiology Group at Boston University School of Public Health

Where are we?

For more information:
email: Dr. Tom Webster, Dept. Environmental Health

return to Tom Webster

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Page last modified on September 24, 2011, at 03:36 PM