In the 19th century and the early part of the 20th century, the worker to Population Ratio was a statistic often used evaluate of how "engaged" a non Christian population was.
Hudson Taylor in China's Spiritual Need and Claims used this measure to evaluate the 18 provinces of China and to show that eleven provinces were largely neglected. At the Edinburgh World Missionary Conference in 1910, it was proposed that the objectives of one missionary for every 50,000 people and one local worker for every 5,000 people would be good ends to work toward, in order to secure sufficient "engagement" of the target population.
These measures are still useful today to measure engagement - though the number of local workers probably would be at least 1,000 people local per worker, having in mind the common saturation church planting goal of one church for every 1,000 people. To determine this ratio, it is necessary to know the population of the target people group, the number of foriegn workers and the number of local workers. This measure should influence the deployment and training of workers