Freedom From Disease sampling plan calculator
This function opens the Graphical User Interface for the FFD sampling plan calculator.
The GUI offers the functionality to
compute first and second-stage sample sizes for two-stage sampling schemes to substantiate freedom from disease,
analyze two-stage sampling schemes with respect to overall cost and sensitivity,
determine cost-optimal strategies and
draw samples from a population.
The GUI is structured into three tabs, Data Input, Parameters, Calculations:
Data Input: The farm data is specified. A list of farms is required with one row per farm and one column containing the herd size, i.e. the number of animals on the farm. The data must be provided in the CSV file format, however currently only the central European format with comma = ",", seperator = ";" is supported. The location of the csv-file is specified in the field Data file, the name of the column containing the herd size is set in the field Herd sizes column via a dropdown menu.
Parameters: Next the survey parameters: design prevalence, Type I error level, intraherd prevalence, and test sensitivity must be set and a sampling strategy (limited sampling or individual sampling, see, e.g. Ziller et al.) must be chosen. Furthermore the cost of each tested herd (excluding the cost per tested animal) and the cost of each tested animal can be specified for cost analyses.
Calculations: Once a sampling strategy is chosen the tab is activated, where cost optimal sampling plans can be determined (Sample size Diagnostics), cost and sensitivity of a fixed sampling schemes can be computed (Compute sample size -> Calculate) and an actual sample can be drawn from the farm file (Compute sample size -> Sample).
The FFD GUI provides the following menu options:
Load loads population data and survey parameter settings from a ffd-RData file.
Save saves population data and survey parameter settings to a ffd-RData file.
Load examples loads built-in examples.
Reset clears all entered data.
R Documentation opens the help file for the FFD GUI (cf
FFD Manual (PDF) opens the pdf manual
About FFD_GUI displays version and developers info.
Cameron A.R. and Baldock F.C. (1998). A new probability formula for surveys to substantiate freedom from disease, Prev. Vet. Med. 34 (1), pp. 1-17
Cameron A.R. and Baldock F.C. (1998). Two-stage sampling in surveys to substantiate freedom from disease, Prev. Vet. Med. 34 (1), pp. 19-30
Ziller M., Selhorst T. Teuffert J., Kramer M. and Schlueter H. (2002). Analysis of sampling strategies to substantiate freedom from disease in large areas, Prev. Vet. Med. 52 (3-4), pp. 333-343