ltdSampling {FFD}

Constructor for class 'LtdSampling'.

Description

Creates an object of the class 'LtdSampling'. For given survey parameters (passed to the function as an object of the class SurveyData) ltdSampling() computes the mean herd sensitivity, the number of herds to test, the expected total number of animals to test and the expected total cost of a survey using limited sampling with a given animal-level sample size sampleSizeLtd. If values for nSampleFixVec and/or probVec are specified, sampling if performed with stratification of the population by risk groups.

Usage

ltdSampling(survey.Data, sampleSizeLtd, nSampleFixVec = NULL, 
	probVec = NULL)

Arguments

survey.Data

Object of class SurveyData. Created by using the function surveyData.

sampleSizeLtd

Positive integer. Pre-fixed number of animals to be tested per holding, irrespective of the herd size (if the herd contains fewer animals then the entire herd needs to be tested).

nSampleFixVec

Numeric vector containing some NAs (optional argument). For risk groups for which the sample size is fixed specify the sample size. For the risk groups for which the sample size should be computed set NA (order of the risk groups must be the same order as in survey.Data@riskValueData).

probVec

Numeric vector. For those risk groups for which the sample size should be computed sample probabilities must be specified. The vector must have the same length as the number of NA entries in nSampleFixVec or if nSampleFixVec is not specified, probVec must have the same length as the number of rows in survey.Data@riskValueData.

Value

The function returns an object of the class LtdSampling.

Author(s)

Ian Kopacka <[e-mail]>

References

A.R. Cameron and F.C. Baldock, "A new probablility formula to substantiate freedom from disease", Prev. Vet. Med. 34 (1998), pp. 1-17.

A.R. Cameron and F.C. Baldock, "Two-stage sampling surveys to substantiate freedom from disease", Prev. Vet. Med. 34 (1998), pp. 19-30.

M. Ziller, T. Selhorst, J. Teuffert, M. Kramer and H. Schlueter, "Analysis of sampling strategies to substantiate freedom from disease in large areas", Prev. Vet. Med. 52 (2002), pp. 333-343.

See Also

See LtdSampling and SurveyData for additional details.

Examples

data(sheepData)
sheepData$size <- ifelse(sheepData$nSheep < 30, "small", "large")
riskValueData <- data.frame(riskGroup = c("small", "large"), 
    riskValues = c(1,2))
mySurvey <- surveyData(nAnimalVec = sheepData$nSheep,
		riskGroupVec = sheepData$size,
		riskValueData = riskValueData,
		populationData = sheepData, designPrevalence = 0.002,
		alpha = 0.05, intraHerdPrevalence = 0.13,
		diagSensitivity = 0.9, costHerd = 30, costAnimal = 7.1)
## Limited sampling without risk groups:    
myLtdSampling <- ltdSampling(survey.Data = mySurvey, sampleSizeLtd = 7)
## Limited sampling with risk groups: 
myLtdSamplingRG <- ltdSampling(survey.Data = mySurvey, sampleSizeLtd = 7, 
	nSampleFixVec = NULL, probVec = c(1,4))