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Manual for psimpoll and pscomb
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Walker & Wilson (1978) argued that
individual curves for pollen types should
be considered independently of each other, especially where the data were
pollen accumulation rates, and therefore statistically independent. They
presented an approach, with FORTRAN programs by Y. Pittelkow, for making
independent splits of the records for individual taxa in a sequence.
The approach involves first identifying portions of the record that are
effectively non-zero sequences, distinguishing them from other portions of
effectively zero sequences. This may be termed presence-absence splitting. The
approach then looks at the non-zero sequences, and splits them
quantitatively with a maximum likelihood method (Walker & Wilson 1978).
Pittelkow's programs implemented the approach in two stages.
In psimpoll I have combined these, making presence-absence splits
first, and
then looking for quantitative splits within non-zero sequences. The detection
of either sort of split is a statistical matter, depending on a level of
significance that is a function of the number of samples
(Walker & Wilson 1978, Table 2) and there may be no splits of
either sort for any given taxon. Splits are ignored if they would create
`zones' of less than 4 samples.
Walker & Pitelkow (1981) present
results using the method from three late Quaternary sequences.
Walker & Wilson (1978)
present curves fitted to portions of the record of particular taxa, identified
from presence-absence and quantitative splitting. However, this was not
included in Pittelkow's programs, and I have not implemented it in
psimpoll.
Instead, I give means and standard deviations for each identified segment of
the record for each taxon.
Results are printed to the screen (possibly too fast to read when plotting
interactively), and to the data analysis file (which must have been
specified: menu Ec). Lines marking the
location of splits are marked across
the plot of each taxon. These are normal lines for quantitative splits,
but dashed lines for presence-absence splits. If pollen zones
are also being incorporated, these
are indicated only by boxes at the righthand end of the plot: marker lines for
the zones are not drawn across the plot.
Independent splitting is carried out as the program is `plotting' each taxon
to the main output file. It is thus necessary to go through with this stage
in order to get any output in the data analyses file.
As presently set up, the process will be carried out on all `taxa'
except summary data, pollen sums, and rate-of-change results. I leave it to
the user to decide whether it is useful or reasonable for items such as
palynological richness!
This option toggles `on' and `off'.
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Copyright © 1995-2007 K.D. Bennett
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