standardization of environmental data and information - International ...

much replication was needed; employing more replication in time and space,
by having more than one control site, would result in a more powerful test. In
the end, however, there would still be some degree of uncertainty, even though
with more replication the certainty might be 0.01 rather than 0.05. He knew
from experience how time-consuming it was to develop a sampling strategy for
pelagic work, and he knew that contractors would never accept having that
many sites. Were they necessary? On the other hand, did the number depend
on the variability between control and impact sites, so that if impacts were
strong, then less replication would be needed?
Etter confirmed that that was true. Power analysis made it possible to
detect how many samples were needed to detect some level of change. That
technique could be used if the level of change was known. Three factors
affected a power analysis: sample size, how big a change was to be detected
and the level of probability of making an error. He encouraged claimants to
perform a power analysis asking whether the proposed replication was
sufficient. If the change was big enough, fewer samples would be necessary,
but that would not be known until someone did a simulation to test what kinds
of impacts to expect.
The same participant also remarked that, while he agreed on the need
for a before-after-control-impact approach to determine whether an impact was
being detected, researchers were also trying to develop a mechanistic
understanding of the functional responses to various types of impacts. In
other words, they were not just looking blindly for an impact based on
statistics; they also hoped to build a predictive model showing what events
would lead to an impact. Such a model could then be tested through BACI
analyses.
Etter agreed that having such models would make it possible to take a
different approach and to optimise the sampling design so that fewer samples
would be needed. That was why he had said that the kinds of experiments
proposed by Smith were an important prerequisite to the rest of the work. In
presenting general sampling designs for detecting environmental impact, he
was not advocating that things had to be done that way; if the other kind of
information was available, different approaches could be taken. However, as
such information was not yet available, he had suggested a basic sampling
strategy.
One participant offered his quick calculation that it would take 21 fast,
experienced taxonomists several years, at the rate of one month per core and
ten working months a year, to examine the nematodes in 216 core samples –
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