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Table 1 List of predictors generated for each model

From: Open-source environmental data as an alternative to snail surveys to assess schistosomiasis risk in areas approaching elimination

Snail survey data model

Environmental predictors model

Presence sites (one or more snails found)

Open data

 Ditches where snails were present

 Built and natural environment

  Distance from home to the nearest identified present ditch (km)

  Distance to nearest waterway (km)

  Total length of present ditches within 0.25 km radius of the home (km)

  Distance to nearest waterbody (km)

  Total length of present ditches within 0.5 km radius of the home (km)

  Distance to nearest road (km)

  Total length of present ditches within 1 km radius of the home (km)

  Elevation (m)

 Fields where snails were present

 

  Distance from home to the nearest identified present field (km)

Remotely sensed data

  Total area of present fields within 0.25 km radius of the home (km2)

 Normalized Difference Water Index (NDWI)

  Total area of present fields within 0.5 km radius of the home (km2)

  Average NDWI within 0.25 km radius of the home

  Total area of present fields within 1 km radius of the home (km2)

  Average NDWI within 0.5 km radius of the home

 

  Average NDWI within 1 km radius of the home

Absence sites (no snails found)

 Normalized Difference Vegetation Index (NDVI)

 Ditches where snails were absent

  Average NDVI within 0.25 km radius of the home

  Distance from home to the nearest identified absent ditch (km)

  Average NDVI within 0.5 km radius of the home

  Total length of absent ditches within 0.25 km radius of the home (km)

  Average NDVI within 1 km radius of the home

  Total length of absent ditches within 0.5 km radius of the home (km)

 Enhanced Vegetation Index (EVI)

  Total length of absent ditches within 1 km radius of the home (km)

  Average EVI within 0.25 km radius of the home

 Fields where snails were absent

  Average EVI within 0.5 km radius of the home

  Distance from home to the nearest identified absent field (km)

  Average EVI within 1 km radius of the home

  Total area of absent fields within 0.25 km radius of the home (km2)

 

  Total area of absent fields within 0.5 km radius of the home (km2)

 Other predictors included in the models

  Total area of absent fields within 1 km radius of the home (km2)

  Number of people tested in the household (N)

Other predictors included in the models

 

 Number of people tested in the household (N)

 
  1. For the snail survey data models, present sites are those where at least one snail was found, while absent sites are those where no snails were found during the 2016 snail surveys. For the environmental data models, NDVI and NDWI were calculated using Landsat-8, Collection 1 satellite data collected on January 23rd, February 8th, and April 28th (dates where there was < 30% cloud cover). Pre-processed EVI data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) Terra satellite was averaged across a total of 12 observations occurring at 16-day intervals between January 1st and July 10th, 2016
  2. NDWI Normalized Difference Water Index, NDVI Normalized Difference Vegetation Index, EVI Enhanced Vegetation Index
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International Journal of Health Geographics

ISSN: 1476-072X