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A two-stage cluster sampling method using gridded population data, a GIS, and Google EarthTM imagery in a population-based mortality survey in Iraq

LP Galway1, Nathaniel Bell2, Al Shatari SAE3, Amy Hagopian4, Gilbert Burnham5, Abraham Flaxman4, Wiliam M Weiss5, Julie Rajaratnam4 and Tim K Takaro1*

Author Affiliations

1 Faculty of Health Sciences, Simon Fraser University, Blusson Hall 8888 University Drive, Burnaby, B.C, Canada V5A 1 S6, USA

2 Department of Surgery, University of British Columbia, West Mall, Vancouver, BC, Canada

3 Human Development and Training Center, Iraqi, Ministry of Health, Iraq

4 School of Public Health, University of Washington, Seattle, WA, USA

5 School of Public Health, Johns Hopkins University, Baltimore, MD, USA

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International Journal of Health Geographics 2012, 11:12  doi:10.1186/1476-072X-11-12

Published: 27 April 2012



Mortality estimates can measure and monitor the impacts of conflict on a population, guide humanitarian efforts, and help to better understand the public health impacts of conflict. Vital statistics registration and surveillance systems are rarely functional in conflict settings, posing a challenge of estimating mortality using retrospective population-based surveys.


We present a two-stage cluster sampling method for application in population-based mortality surveys. The sampling method utilizes gridded population data and a geographic information system (GIS) to select clusters in the first sampling stage and Google Earth TM imagery and sampling grids to select households in the second sampling stage. The sampling method is implemented in a household mortality study in Iraq in 2011. Factors affecting feasibility and methodological quality are described.


Sampling is a challenge in retrospective population-based mortality studies and alternatives that improve on the conventional approaches are needed. The sampling strategy presented here was designed to generate a representative sample of the Iraqi population while reducing the potential for bias and considering the context specific challenges of the study setting. This sampling strategy, or variations on it, are adaptable and should be considered and tested in other conflict settings.

Cluster sampling; Population-based survey; Mortality; Conflict; Iraq war; Geographic information system (GIS); Google EarthTM