B.Precision levels and sampling intensities
1.Where it is not possible to define quantitative targets for sampling programmes, neither in terms of precision levels, nor in terms of sample size, pilot surveys in the statistical sense shall be established. Such pilot surveys shall evaluate the importance of the problem and shall also address the utility of future more detailed surveys, and the cost-effectiveness relationship of such detailed surveys.
2.Where quantitative targets can be defined, they may be specified either directly by sample sizes or sampling rates, or by the definition of the levels of precision and of confidence to be achieved.
3.Where reference is made to a sample size or to a sampling rate in a population defined in statistical terms, the sampling strategies shall be at least as efficient as Simple Random Sampling. Such sampling strategies shall be described within the corresponding national programmes.
4.Where reference is made to precision/confidence level the following distinction shall apply:
(a) Level 1
:
level making it possible to estimate a parameter either with a precision of plus or minus 40 % for a 95 % confidence level or a coefficient of variation (CV) of 20 % used as an approximation;
(b) Level 2
:
level making it possible to estimate a parameter either with a precision of plus or minus 25 % for a 95 % confidence level or a coefficient of variation (CV) of 12,5 % used as an approximation;
(c) Level 3
:
level making it possible to estimate a parameter either with a precision of plus or minus 5 % for a 95 % confidence level or a coefficient of variation (CV) of 2,5 % used as an approximation.