Another story of success driven by better measurement is polio. Starting in 1988, global health organizations (along with many countries) established a goal of eradicating polio, which focused political will and opened purse strings to pay for large-scale immunization campaigns. By 2000, the virus had nearly been wiped out; there are now fewer than 1,000 cases world-wide.

But getting rid of the very last cases is the hardest part. In order to stop the spread of infections, health workers have to vaccinate nearly all children under the age of 5 multiple times a year in polio-affected countries. There are now just three countries that have not eliminated polio: Nigeria, Pakistan and Afghanistan. I visited northern Nigeria four years ago to try to understand why eradication is so difficult there. I saw that routine public health services were failing: Fewer than half the kids were getting vaccines regularly. One huge problem was that many small settlements in the region were missing from vaccinators’ hand-drawn maps and lists documenting the locations of villages and numbers of children.

To fix this, the polio workers walked through all high-risk areas in the northern part of the country, which enabled them to add 3,000 previously overlooked communities to the immunization campaigns. The program is also using high-resolution satellite images to create even more detailed maps. As a result, managers can now allocate vaccinators efficiently.

What’s more, the program is piloting the use of phones equipped with a GPS application for the vaccinators. Tracks are downloaded from the phone at the end of the day so managers can see the route the vaccinators followed and compare it to the route they were assigned. This helps ensure that areas that were missed can be revisited.