Ce programme calcule le nombre approximatif de pools requis pour une gamme de tailles de pools et de valeurs spécifiées pour la prévalence estimée ainsi que pour la confiance et la précision souhaitées de l'estimation, en supposant des tailles de piscine fixes et un test avec 100% de sensibilité et de spécificité. Voir Worlund & Taylor (1983) for more details.
The required number of pools (m) to estimate the true prevalence with the desired precision is
calculated as:
où:
For fixed pool size and perfect tests, the optimum value of m can be calculated that minimises the variance of the estimated prevalence and consequently minimises the number of pools requiring testing to achieve the desired confidence and precision. This optimum value for m depends on the prevalence and is approximately 1.6/pi. This equates to the pool size which results in an expected number of 1.6 infected individuals per pool. See Sacks et al. (1989) for more details. Prevalence estimates may be upwardly biased, particularly as the probability of all pools testing positive increases (high prevalence and/or small numbers of large pools). Therefore, it is advisable to select a lower value for pool size and test a larger number of smaller pools to minimise potential bias in the result.
Les entrées requises pour cette analyse sont:
For example, you might wish to estimate the prevalence where the true value is assumed to be about 0.01 (1%), and you wish to have 95% (0.95) confidence that the true value is within +/- 0.005 (0.5%) of your estimate. The assumed prevalence, desired precision and level of confidence must all be >0 and <1.
You can also input a suggested pool size if desired, and the program will calculate the corresponding number of pools to be tested for that pool size (in addition to predetermined pool sizes). Suggested pool size is ignored if it is zero.
Le résultat de l'analyse est: