4.1 The ideal method for compliance monitoring is a procedure that:

.1 detects organisms in the ballast water discharge;

.2 has an appropriate limit of detection;

.3 is precise;

.4 is accurate;

.5 is economical;

.6 is quick;

.7 can be carried out with minimal technical expertise; and

.8 can be obtained in all parts of the world.
However, any result obtained would have to include confidence limits based
on both the sampling error and analytical error.
4.2 Sources of error include, but are not limited to, errors arising
within:
4.3 The variation arising from sampling should be added to that from
analysis to determine the confidence limits within which the true value of the organism
number lies. This has an important bearing on how the result can be used for enforcement
of the BWM
Convention.
4.4 The sampling uncertainty can be obtained by setting up a
null–hypothesis, that is a general or default position that is expected in the results,
e.g. the average concentration of organisms is equal to the D2 standard at a selected
level of significance and then the data would be analysed using one of the following
tests:
Table 1: Statistical handling of
the results
Distribution of the results

Test

Notes

Normal distribution

ttest

It is unlikely this test will be used, as it is
not used with "rare" populations, i.e. the expected population of organisms
in treated ballast water

A distribution that is not normal

Nonparametric Wilcoxon rank test

Not normal due to the small number of
samples

Poisson distribution

Chisquare test

Used when the analytical results are treated as
one sample (i.e. the numbers of organisms over the entire volume are very
rare [low] and combined).

Ideally, an analysis of the distribution should be performed before the
data are statistically evaluated.
4.5 There has been much discussion within the IMO on whether the results of
the analysis should be averaged to assess compliance or that every result should have to
meet the D2 standard. This is a unique debate at IMO due to the biological nature of
the subject matter being analysed, and different States have significantly different
views on this issue. Therefore, it will be very difficult to arrive at a conclusion as
in the case of noncompliance the results of the analysis are likely to be used in the
legal jurisdictions of each IMO Member State, and each of those States may require
different evidence to support any enforcement action.
4.6 If the results of detailed analysis are to be averaged, then both the
sample variation and the analysis variation need to be calculated and applied to the
result. However, some analysis of the sample variation may be needed, as it may be
unacceptably high. For example, for five treated ballast water samples, viable organism
number results of 9,9,9,9 and 9 will provide the same average as 0,0,0,0 and 45. Both
systems would pass the D2 standard, if averaged; however, the variation is considerably
bigger for the second set of results and may prove to be unacceptable because of the one
large value.
4.7 If each of the results is treated as an individual value that has to
meet the D2 standard, then again the confidence limits would have to be calculated from
the sampling and analytical errors. Here if all results are less than the D2 standard,
then the sampling has proved that the BWMS is meeting the standard.
4.8 The basic difference between instantaneous and average approaches is
that the results of the average approach describe the variations of the concentration of
organisms during the deballasting event, whereas the results of the instantaneous
approach describes the variation based on the assumptions of the Poisson distribution.
However, the average approach, based on the results of a few samples, has the
disadvantage that the variation may be too high, is unacceptable and needs to be
improved, which could invalidate the evaluation and lead to inconclusive results.
4.9 The instantaneous approach has the disadvantage that variations in the
organism levels at different times of the discharge are not taken into account, which
should not be a problem if all the samples meet the D2 standard. If the discharge is
not always under the D2 standard, the problem can be mitigated by using a
flowintegrated sample over set periods of time, which, if taken properly, represents an
average of the organisms in the treated ballast water over that time when presented with
variance estimates and confidence intervals. This constitutes a better representation of
the ballast water quality than separate samples. In addition, a lower variation should
be obtained because a larger sample is being analysed. The average approach is likely to
have the same disadvantages unless the samples are very large and collected over most of
the discharge.
4.10 The differences between applying an instantaneous sampling regime or
an average sampling regime to the result are less extreme when taking numerous
flowintegrated samples. This is because for each discharge there will be a number of
results arising from samples that have been averaged over a specific time.