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USING GIS TO ESTIMATE HOW MOTHERS’ BREASTFEEDING DECISIONS RESPOND TO EXPOSURE TO ARSENIC-CONTAMINATED DRINKING WATER
KARTINI SHASTRY (WITH PINAR KESKIN AND HELEN WILLIS) GIS DAY 2015, WELLESLEY COLLEGE
MOTIVATION AND RESEARCH QUESTION
Breastfeeding has health benefits for infants when water-related diseases/contaminants are prevalent
Do mothers increase duration of breastfeeding in response to concerns about water quality? Context: millions of people in Bangladesh exposed
to arsenic in their drinking water
1970’s: millions of tube wells installed
1990’s: arsenic discovered in many tube wells
1999-2006: information campaign, tested wells, painted contaminated wells red
HISTORY OF SAFE DRINKING WATER IN BANGLADESH
OVERVIEW: STRATEGY AND RESULTS
Sources of variation Compare children born before and after campaign Compare children living in more and less contaminated
villages Geography of contamination means that people in different
villages have varying access to uncontaminated water, even conditional on exposure
Mothers breastfeed children longer More likely to breastfeed infants exclusively Improved health for infants (reduced mortality rate, reduced
diarrheal incidence)
THE DATA CHALLENGE
Data on children born 1995-2007 (Bangladesh DHS) GPS coordinates of village
Need measures of arsenic exposure and access to clean water
Two imperfect sources of data on arsenic levels of wells 1. Original data: British Geological Society (BGS)
3500 wells with GPS coordinates, covers entire country
2. New data: Bangladesh Arsenic Mitigation Water Supply Program (BAMWSP) 4.5 million wells but no GPS coordinates, doesn’t cover entire country
Does have mouza identifer (village cluster)
BGS VS BAMWSP DATA
1998-1999 Tested 3,500 wells
ORIGINAL DATA 1 POINT=1 WELL
NEW DATA 1 POINT=20-30WELLS
1999-2004 Tested 4.5 million wells
Many mouzas that do not appear in the BAMWSP well data are ‘arsenic safe’ on this online map
SOME MISSING MOUZAS CONSIDERED SAFE
MISSING MOUZAS IN CONTAMINATED AREAS
Original Data DHS village locations BGS wells
Mouzas shaded by number of wells tested
New Data
Mouzas
shaded by mean As level of tested wells
RESULTS WITH MEASURE OF EXPOSURE
Exposure ~ fraction of wells contaminated Exposure measures highly correlated
ρ ranges from 0.69 - 0.99 Predict household-level arsenic measures
Main results with new measures are consistent In fact, magnitudes are remarkably similar
MEASURING ACCESS TO CLEAN WATER
Estimate access to clean water, conditional on exposure to arsenic-contaminated water Requires more precise information on well’s location
Better to have GPS location or larger sample of wells ???
Option 1: “Inverse Distance Weighting” (IDW, Krigging) Interpolate As level ‘everywhere’ using mean As of wells tested in
a mouza, assigning all of them to the ‘center’ of the mouza
OUTPUT OF INVERSE DISTANCE WEIGHTING
Some villages have better access to clean wells than others
MEASURING ACCESS TO CLEAN WATER
Estimate access to clean water, conditional on exposure to arsenic-contaminated water Requires more precise information on well’s location
Better to have GPS location or larger sample of wells ???
Option 1: “Inverse Distance Weighting” (IDW) or Krigging Interpolate As level ‘everywhere’ using mean As of wells tested in
a mouza, assigning all of them to the ‘center’ of the mouza
Option 2: Simulate measures Distribute tested wells to randomly chosen points in a mouza
GPS DATA BETTER THAN LARGE SAMPLE
All measures seem to relate nicely with each other and with household-level arsenic measures
BGS measures do a slightly better job at predicting who continues to use contaminated water (slightly higher R-squared)
New measures too highly correlated with contamination to estimate triple difference
The End!