You could start by examining the home location of beneficiaries from record cards. You could map these or just tally them up as "in town" and "out of town". You could easily take a pretty large sample (e.g. n >= 96) and estimate the proportion coming from outside the town. An issue with this approach that you have to work out if this is a good thing or a bad thing. It may be (e.g.) that there are few cases attending from inside the town because there really are few SAM cases inside the town (i.e. the prevalence of SAM is much lower in the town than out of the town). I think you could answer this by doing some case-finding in the town. You might frame this as "coverage in the town is below X%" type of hypothesis. Case-finding in surveys in towns is not easy. This is covered (a bit) in the SQUEAC / SLEAC Technical reference. One approach is to sample town blocks and do house-to-house screening in selected city blocks. A purposive sample of blocks (i.e. the poorer areas) with house-to-house sampling in these blocks might be easier. I hope this helps.