Answers
Method 1:
Let us specifically choose any country to find what population is affected by Covid19. So I will Partition the entire area of Country according to density of population(More partitions will be better). The screening test should be conducted at each and every airport, stations, stands, etc to get general Idea about what proportion of passengers travelling from particular city or country are affected. Then we can trace each and every person with whom positive patient has been in contact for last 15 days.
I can then calculate mean estimate for each region that I have partitioned. This is one crude method.
Method 2:Now the cases of covid19 are more in cities than rural areas.
So we can do the systematic sampling in rural areas where we can select samples according to some specific pattern in villages and tests them. If any village has proportion larger than some pre specified threshold then we can conduct large number of tests for that village.
For cities, most of the patients would have travel history from other countries so we can screen them at airport and conduct the tests.
Challenges-Well there might be some cases which we may not encounter.And because this covid spreads by coming in contact with that person, the cases may get increase rapidly.
So what we can do is to carry out tests as large as possible in number just to get fair idea about the spread of the disease. Once we have enough samples tested we can say with high likelihood if any particular region is under danger zone or not.
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