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# Estimating Coverage

This question was posted the Assessment and Surveillance forum area and has 4 replies.

### Ernest Guevarra

Technical expert

24 Jul 2012, 10:15

### Saul Guerrero

Director of Nutrition

Normal user

24 Jul 2012, 10:30

Hi Ernest Thanks for that answer - the team involved will appreciate it. A point of clarification about the process: the project works in 4 "sectors" of a city. The hypothesis was about the coverage within the entire sector (i.e. 3 were high coverage sectors, 1 was low coverage sector). Each sector has about 4-5 sub-sectors; what the team did was to randomly select a sub-sector from each of the 4 sectors, and to do house-to-house case-finding there. I hope that clarifies how the process was carried out Appreciate the support on the calculation of the CI S

### Saul Guerrero

Director of Nutrition

Normal user

24 Jul 2012, 10:30

Hi Ernest Thanks for that answer - the team involved will appreciate it. A point of clarification about the process: the project works in 4 "sectors" of a city. The hypothesis was about the coverage within the entire sector (i.e. 3 were high coverage sectors, 1 was low coverage sector). Each sector has about 4-5 sub-sectors; what the team did was to randomly select a sub-sector from each of the 4 sectors, and to do house-to-house case-finding there. I hope that clarifies how the process was carried out Appreciate the support on the calculation of the CI S

### Mark Myatt

Frequent user

24 Jul 2012, 18:51

I think you could just use the data you have. Assuming that ... ``` n = number of cases c = number of covered cases ``` The coverage proportion p can be estimated as: ``` p = c / n ``` with c and n calculated for point of period coverage as appropriate. Given that you have such a large sample size, a 95% CI can be can be calculated as: ``` 95% CI = p +/- 1.96 * sqrt((p * (1 - p) / n)) ``` A worked example: ``` n = 600 c = 240 p = c / n = 240 / 600 = 0.4 95% CI = 0.4 +/- 1.96 * sqrt((0.4 * (1 - 0.4) / 600)) = 0.4 +/- 1.96 * sqrt((0.4 * 0.6) / 600) = 0.4 +/- 0.0392 = 0.3608; 0.4392 ``` Multiply all by 100 to get percentages (in the worked example ... coverage = 40.0%, 95% CI = 36.1%; 43.9%).