Inverse sampling to study disease burden of leprosy

Estimation of disease burden due to leprosy by conventional sampling procedure is difficult due to large sample size requirement. In such situation, inverse sampling procedure could be a choice. A pilot study was undertaken to study the feasibility of adopting inverse sampling procedure over conventional sampling in an endemic area of Uttar Pradesh, India.

Two community development blocks one with high endemic, namely, Fatehganj, and other low endemic, Ramnagar, in Bareilly district of Uttar Pradesh, India, were selected. The Inverse sampling was adopted in Fatehganj and conventional cluster sampling was used in Ramnagar. As per the design of inverse sampling, 25 new cases of leprosy were to be detected from a population that could provide the cases. Under conventional sampling, a sample of 44,000 subjects (population) was targeted for the survey.

In Fatehganj, 25 new cases of leprosy were detected from a sample of 14734 individuals. In Ramnagar, a total of 63 new cases of leprosy were found after covering a sample of 44686 individuals. Both the techniques provided similar estimates. The precision obtained under inverse sampling was though less than that under conventional sampling but found to be more feasible and suitable for estimation of leprosy due to less population to be covered, time and cost.

Our findings showed reveals that inverse sampling was advantageous over conventional sampling and could be adopted for the large scale survey at national level.