n.rb.2stage.1: sample size for 2-stage risk-based surveillance, risk factor...

Description Usage Arguments Value Examples

View source: R/n_rb2stage.R

Description

Calculates sample size required (clusters and units) for a 2-stage risk-based survey with a single risk factor at the cluster level only.

Usage

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n.rb.2stage.1(rr, ppr, spr, pstar.c, pstar.u, se = 1, sep.c = 0.95,
  sep.sys = 0.95)

Arguments

rr

relative risk values (vector of values, corresponding to the number of risk strata)

ppr

population proportions corresponding to rr values (vector of equal length to rr)

spr

planned surveillance proportions corresponding to rr values - the proportions of the total sample to be collected from each risk stratum (vector of equal length to rr).

pstar.c

cluster (herd) level design prevalence, scalar, either proportion or integer

pstar.u

unit (animal) level design prevalence, scalar, either proportion or integer

se

unit sensitivity of test (proportion), scalar, default = 1

sep.c

desired cluster-level sensitivity (proportion), scalar, default = 0.95

sep.sys

desired population-level sensitivity (proportion), scalar, default = 0.95

Value

A list of seven elements: 1) a vector (of the same length as rr) of the numbers of clusters to sample from each risk stratum, 2) the total number of clusters to be sampled, 3) a vector of EPI values for each risk stratum, 4) a vector of adjusted risk values for each risk stratum, 5) the number of untis to be sampled per cluster 6) a vector of the total numbers of units to be sampled for each risk stratum 7) the overall total number of units to be sampled

Examples

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rr<- c(5,3,1)
ppr<- c(0.1, 0.2, 0.7)
spr<- c(0.4, 0.4, 0.2)
n.rb.2stage.1(rr, ppr, spr, pstar.c=0.01, pstar.u=0.1, se =0.9, sep.c=0.8, sep.sys=0.95) 
n.rb.2stage.1(c(3,1), c(0.2,0.8), c(0.7,0.3),0.05, 0.1, 0.9, 0.95, 0.99)

Example output

$n
[1] 79 79 39

$total
[1] 197

$epi
[1] 0.027777778 0.016666667 0.005555556

$adj.risk
[1] 2.7777778 1.6666667 0.5555556

$units
[1] 18

$risk.units
[1] 1422 1422  702

$total.units
[1] 3546

$n
[1] 39 16

$total
[1] 55

$epi
[1] 0.10714286 0.03571429

$adj.risk
[1] 2.1428571 0.7142857

$units
[1] 32

$risk.units
[1] 1248  512

$total.units
[1] 1760

RSurveillance documentation built on May 29, 2017, 11:52 p.m.