Quality Assuarance Officer
Normal user
5 Sep 2013, 07:47
We are doing a sort of follow up coverage assessment after two years of CMAM program. The project had a baseline coverage estimate in 2011 (used CSAS). The project targets >70% coverage by now. So, how shall we approach the task?
1. Use the one point 50%+/-10%
2. Use the classical difference of two proportions estimation and correct for size
3. any other way which I am not clear
Thanks for your support
Frequent user
5 Sep 2013, 09:54
There are a few ways to do this.
(A) A full SQUEAC. This will give you a lot of information on barriers to coverage as well as a coverage estimate.
(B) A plain CSAS. You'd probably want to aim for a sample size suitable to estimating a proportion of 70% with a useful precision (i.e. +/- 10 or better). For this you'd need a sample size of 80 or more.
(C) A Bayesian CSAS. This is as above but you can factor in what you already know about coverage from your previous CSAS, routine monitoring data, &c. to give a prior. You would combine this prior with new CSAS data using a beta-binomial conjugate analysis. The advantage of this approach is that you would need a smaller sample size as the prior contributes information. If (e.g.) you had a reasonable believe that coverage was most likely to be about 70% and very unlikely to be below 50% and extremely unlikely to be above 90% then a sample size of n = 42 might suffice to give you 10% precision whilst retaining some protection against bias from a misspecified prior. Details of this approach can be found in the
SQUEAC / SLEAC technical reference and software is available
here.
(D) Use SLEAC. This is a cut-down CSAS type survey that provides a classification. A typical sample size is n = 40. Details of this approach can be found in the
SQUEAC / SLEAC technical reference.
I hope this is of some use.