epi.simplesize {epiR} | R Documentation |
Estimates the required sample size under under simple random sampling.
epi.simplesize(N = 1E+06, sd, epsilon, method = "mean", conf.level = 0.95)
N |
scalar, representing the population size. |
sd |
scalar, if method is total or mean this is the estimated standard deviation of the sampling variable. If method is proportion this is an estimate of the unknown population proportion. |
epsilon |
the maximum absolute difference between our estimate and the unknown population value. |
method |
a character string indicating the method to be used. Options are total , mean , or proportion . |
conf.level |
scalar, defining the level of confidence in the computed result. |
Returns an integer defining the size of the sample is required.
If the calculated sample size is greater than 10% of the population, an adjusted sample size is returned.
Levy PS, Lemeshow S (1999). Sampling of Populations Methods and Applications. Wiley Series in Probability and Statistics, London, pp. 70 - 75.
Scheaffer RL, Mendenhall W, Lyman Ott R (1996). Elementary Survey Sampling. Duxbury Press, New York, pp. 95.
## EXAMPLE 1 ## We want to estimate the mean bodyweight of deer on a farm. There are 278 ## animals present. We anticipate the standard deviation of body weight to be ## around 30 kg. We would like to be 95% certain that our estimate is within ## 10 kg of the true mean. How many deer should be sampled? epi.simplesize(N = 278, sd = 30, epsilon = 10, method = "mean", conf.level = 0.95) ## A sample of 31 deer are required. ## EXAMPLE 2 ## We want to estimate the seroprevalence of Brucella abortus in a population ## of cattle. An estimate of the unknown prevalence of B. abortus in this ## population is 0.15. We would like to be 95% certain that our estimate is ## within 20% of the true proportion of the population that is seropositive ## to B. abortus. Calculate the required sample size. ## Convert relative error into absolute error: sd <- 0.15 epsilon.r <- 0.20 epsilon <- epsilon.r * sd epi.simplesize(N = 1E+06, sd = sd, epsilon = epsilon, method = "proportion", conf.level = 0.95) ## A sample of 544 cattle are required.