title: Using satellite imagery and GPS technology to create random sampling frames in high risk environments.
abstract: BACKGROUND
  Health surveys are important tools for assessing needs and informing policy decisions. However, obtaining representative samples is challenging in environments without traditional infrastructure or census data. We describe a method using satellite imagery, geographic information systems and GPS technology to obtain an accurate sample of such a population.
  
  
  METHODS
  The Kerenik Camp in Darfur is a conflict-heavy environment with 25,000 internally displaced persons (IDPs). We requisitioned high-resolution satellite imagery of the camp prior to arrival. Structures identified as potential domiciles were geocoded with a unique ID and coordinate. A random selection of ID numbers formed the representative sample. Researchers visited these coordinates using handheld GPS devices and administered surveys to the inhabitants.
  
  
  RESULTS
  2219 geocoded points were visited. Of these, 1655 (74.6%) proved to be unique domiciles. Our survey participation rate was 87.1%. The overall effective rate of completed survey per geocoded point visited was 39.1%.
  
  
  CONCLUSIONS
  Our sampling technique offers several advantages when surveying vulnerable populations. It permits the establishment of a sampling frame without need for traditional infrastructure, such as addresses or telephones. Sampling frames can be constructed remotely and prior to survey initiation, important considerations for insecure environments where time on the ground may be limited.
  
  
  CONCLUSIONS
  This technique can be used for any setting requiring a random sample, but is especially useful in insecure environments and survey areas without accessible census data, postal addresses, or telephone numbers. Sampling frames can be constructed remotely and prior to survey initiation, important considerations for environments where time on the ground may be limited.
authors.affiliation: University of Colorado School of Medicine, Department of Surgery, 12631 E. 17th Ave, C302, Aurora, CO, 80045, USA. Electronic address: yihan.lin@mail.harvard.edu.
authors.forename: Yihan
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Woodrow Wilson School of Public & International Affairs, Princeton University, Robertson Hall, Princeton, NJ, 08540, USA. Electronic address: david.kuwayama@ucdenver.edu.
authors.forename: David Paul
authors.initials: DP
authors.lastname: Kuwayama
mesh_terms: D003906:Developing Countries; D040362:Geographic Information Systems; D006306:Health Surveys; D006801:Humans; D012424:Rural Population; D063809:Satellite Imagery; D013397:Sudan / Q000453:epidemiology; D035862:Vulnerable Populations
keywords: GPS; Geocode; Geographic information systems; Health questionnaire; Health survey; Imagery; Internally displaced; Person; Refugee; Sampling frame; Satellite