canberrabirds
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To: | <> |
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Subject: | Further to Quest for the breeding K Parrot |
From: | "Philip Veerman" <> |
Date: | Sun, 6 Feb 2011 16:20:11 +1100 |
My
apologies for another message about this but it is important (in case anyone has
a serious interest in understanding these data) to explain another important
reason why Martin's graph did not match mine.
My
comments were based on breeding results as tallied by breeding records in the
GBS. Martin's graph and comments were based on breeding results as tallied by
breeding observations in the GBS. This was clear from Martin's comments and
the scale on the graph leaves me with no doubt that is what it shows but even I
missed the point and no one has commented on this.
These
are potentially very different things, as one breeding record can have from 1 to
52 breeding observations. Although for this species it is typically 1 or 5 to
10. This is all explained in The GBS Report. Basically a record is at least one
observation of an event on one chart. An observation is one entry on one week.
For example the Ravens breeding at my house this year have 19
breeding observations this year. But from watching them
I know there is only one breeding event (one pair raising 3 chicks) and
thus one record. In terms of the incidence of local breeding, which surely is
the relevant question about the King Parrots, I believe that number of records
is far more accurate than the number of observations. It is almost certain that
for this species many observations are still just one breeding event, as in
repeated noting of the same family over several weeks. Not only that but it
is important to note that the number of observations
introduces a whole extra huge aspect of survey randomness because it depends on
observer activity and how many weeks the observer is present (in my raven case
the 2 weeks missing of the year are when I was away).
MS
Access is great for counting numbers of records fitting various criteria in the
database. So the MS Access report I
mentioned: "Breeding records and ratios by species and year" is really easy to
output (once the query structure had been built). Martin's output, that counted observations, as in
fields (weeks) containing an entry in each record is considerably more complex
to extract, although I don't know his method (probably from Countif function
after exporting to Excel). Counting observations is very useful for
some purposes, such as obviously to produce the graphs showing the timing of the
various stages of breeding for the 18 species
with the most breeding records shown in the 21 Year editions of The GBS Report
(referred to as the Breeding Graphs). However in addition to my earlier
note, for these reasons, I recommend that it is flawed in terms of answering the
question that Martin was addressing, which was about incidence of local
breeding.
My apologies also for earlier writing in terms of "the
data", rather than "these data". I often forget that the word "data" is
plural.
Philip
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