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Risk-based sample size calculation for consecutive surveys to document freedom from animal diseases
Heinzpeter Schwermer1, Isabel Reding, Daniela C Hadorn
1Swiss Federal Veterinary Office, Schwarzenburgstrasse 155, CH-3003 Bern, Switzerland. heinzpeter.schwermer@bvet.admin.ch
Preventive Veterinary Medicine
|September 19, 2009
Summary
Risk-based sample size calculations for disease freedom documentation reduce survey costs and sample sizes. This method optimizes repeated surveys by incorporating historical data and import risk assessments, cutting annual survey sizes by 25%.
Area of Science:
- Veterinary epidemiology
- Quantitative risk assessment
- International trade compliance
Background:
- International trade necessitates documented disease freedom, typically via national surveys.
- Traditional random sampling for disease freedom surveys is costly and may not be efficient for repeated assessments.
- Existing risk-based sample size calculations are primarily for single surveys, not consecutive applications.
Purpose of the Study:
- To develop a risk-based sample size calculation method for consecutive surveys to document freedom from non-highly contagious diseases.
- To incorporate the time value of historical testing data, import risks, and within-country disease spread into sample size calculations for repeated surveys.
- To enhance the efficiency and reduce the costs of disease freedom documentation through optimized survey planning.
Main Methods:
- Devised a risk-based sample size calculation framework for sequential disease surveys.
- Incorporated calculation of confidence loss due to disease import and undetected disease between surveys.
- Developed a process to calculate the time value of information from historical surveys for consecutive risk-based sample size calculations.
Main Results:
- The proposed risk-based method accounts for confidence reduction between surveys by considering import risk and disease spread.
- Historical testing information's time value is adjusted and integrated into the sample size calculation for repeated surveys.
- Annual surveys utilizing this risk-based approach, including import risk assessments and adjusted time value of information, demonstrated a 25% reduction in sample size compared to non-risk-based methods.
Conclusions:
- The developed risk-based sample size calculation is suitable for consecutive surveys requiring disease freedom documentation.
- This method effectively estimates confidence reduction between surveys and optimizes sample sizes.
- Implementing this approach can significantly reduce sample sizes and associated costs for repeated disease surveillance efforts.
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