Coverage Monitoring Network
CMAM COVERAGE MONITORING
Improving nutrition programmes through the promotion of quality coverage assessment tools, capacity building and information sharing.
What is the difference between point and period coverage? Which one should be used?
Two estimators of coverage are in common use:
Point coverage: this estimator uses data for current cases only. It provides a snapshot of service performance and places a strong emphasis on the timeliness of case finding and recruitment. Point coverage is calculated using the following formula:
Period coverage: this estimator uses data for both current and recovering cases. Recovering cases are children that should be receiving treatment because they have not yet met discharge criteria. Period coverage is calculated using the following formula:
The point coverage estimator can give a misleading picture of coverage in a service with high coverage given its good case-finding and recruitment and short lengths of stay. In such cases the two estimators will yield very different results. For example, a survey found:
Number of SAM cases in the community: 2
Number of SAM cases in treatment: 0
Number of recovering cases in treatment: 34
The point coverage estimator returns:
but the period coverage estimator returns:
In this example the period coverage estimator is probably the better indicator of coverage. In this example, the point coverage estimate penalises good performance.
The period coverage estimator can give a misleading picture of coverage in services with poor case-finding and recruitment and long lengths of stay due to late presentation and / or late admission. In such cases the two estimators will yield very different results. For example:
Number of SAM cases in the community: 12
Number of SAM cases in treatment: 3
Number of recovering cases in treatment: 22
The point coverage estimator returns:
but the period coverage estimator returns:
In this example the point coverage estimator is probably the better indicator of coverage.
The overall coverage estimate varies with the estimator used and results can be difficult to interpret without contextual information.
The choice of estimator to report should therefore be informed by context:
Period coverage: this estimator uses data for both current and recovering cases. Recovering cases are children that should be receiving treatment because they have not yet met discharge criteria. Period coverage is calculated using the following formula:
The point coverage estimator can give a misleading picture of coverage in a service with high coverage given its good case-finding and recruitment and short lengths of stay. In such cases the two estimators will yield very different results. For example, a survey found:
Number of SAM cases in the community: 2
Number of SAM cases in treatment: 0
Number of recovering cases in treatment: 34
The point coverage estimator returns:
but the period coverage estimator returns:
In this example the period coverage estimator is probably the better indicator of coverage. In this example, the point coverage estimate penalises good performance.
The period coverage estimator can give a misleading picture of coverage in services with poor case-finding and recruitment and long lengths of stay due to late presentation and / or late admission. In such cases the two estimators will yield very different results. For example:
Number of SAM cases in the community: 12
Number of SAM cases in treatment: 3
Number of recovering cases in treatment: 22
The point coverage estimator returns:
but the period coverage estimator returns:
In this example the point coverage estimator is probably the better indicator of coverage.
The overall coverage estimate varies with the estimator used and results can be difficult to interpret without contextual information.
The choice of estimator to report should therefore be informed by context:
- If there is good case-finding and recruitment (i.e. SAM cases found early in the stage of the disease) and short lengths of stay then the period coverage estimator is likely to be appropriate.
- If there is poor case-finding and recruitment (i.e. SAM cases found late in the stage of the disease) and long lengths of stay due to late presentation and / or late admission then the point coverage estimator is likely to be appropriate.