Description Usage Arguments Value Note References Examples

View source: R/epi.sssimpleestc.R

Sample size to estimate a continuous outcome using simple random sampling.

1 2 | ```
epi.sssimpleestc(N = 1E+06, xbar, sigma, epsilon, error = "relative",
nfractional = FALSE, conf.level = 0.95)
``` |

`N` |
scalar integer, representing the total number of individual listing units in the population. |

`xbar` |
scalar number, the expected mean of the continuous variable to be estimated. |

`sigma` |
scalar number, the expected standard deviation of the continuous variable to be estimated. |

`epsilon` |
scalar number, the maximum difference between the estimate and the unknown population value expressed in absolute or relative terms. |

`error` |
character string. Options are |

`nfractional` |
logical, return fractional sample size. |

`conf.level` |
scalar number, the level of confidence in the computed result. |

Returns an integer defining the required sample size.

If `epsilon.r`

equals the relative error the sample estimate should not differ in absolute value from the true unknown population parameter `d`

by more than `epsilon.r * d`

.

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.

Otte J, Gumm I (1997). Intra-cluster correlation coefficients of 20 infections calculated from the results of cluster-sample surveys. Preventive Veterinary Medicine 31: 147 - 150.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | ```
## EXAMPLE 1:
## A city contains 20 neighbourhood health clinics and it is desired to take a
## sample of clinics to estimate the total number of persons from all these
## clinics who have been given, during the past 12 month period, prescriptions
## for a recently approved antidepressant. If we assume that the average number
## of people seen at these clinics is 1500 per year with the standard deviation
## equal to 300, and that approximately 5% of patients (regardless of clinic)
## are given this drug, how many clinics need to be sampled to yield an estimate
## that is within 20% of the true population value?
pmean <- 1500 * 0.05; psigma <- (300 * 0.05)
epi.sssimpleestc(N = 20, xbar = pmean, sigma = psigma, epsilon = 0.20,
error = "relative", nfractional = FALSE, conf.level = 0.95)
## Four clinics need to be sampled to meet the requirements of the survey.
## EXAMPLE 2:
## We want to estimate the mean bodyweight of deer on a farm. There are 278
## animals present. We anticipate the mean body weight to be around 200 kg
## and the standard deviation of body weight to be 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.sssimpleestc(N = 278, xbar = 200, sigma = 30, epsilon = 10,
error = "absolute", nfractional = FALSE, conf.level = 0.95)
## A total of 31 deer need to be sampled to meet the requirements of the survey.
``` |

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