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Originally Posted by
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But a very large sample (around 10,000) [
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in relation to
surrounding habitat, within garden practices and geographic location.
Please tell us how you work that out?
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The survey collects the relevant information.
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Although there is variation in the ability of individual participants,
and in the amount of time they spend carrying out the recording, our
statistical models typically include a site-effect, which enables us to
control for this variation. From a statistical perspective, the sheer
size of the project increases its robustness, since it is the underlying
patterns that are important.
Have you ever tried to count sparrows coming and going in a garden?
We have loads of them and I defy anyone to count them and know whether
the same ones are counted over and over again?
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Counting is on the basis of the maximum number of birds seen at one time (which is a lower bound on the actual number of birds). But many analyses are simply looking at presence or absence of a species, and actual numbers are irrelevant to this.
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