Dear friends,
The the latest version of ASREML contains an extension to the spline
option which you should be aware of. I am indebted to Robin Thompson
and Ian White for working out the details.
The syntax
datafilename
Y ~ mu X !r spl(X)
will now produce a spline with no more than 50
knot points (previously the default was 100).
If there are 50 or more unique X values, ASREML will use 50 equi-distant
knot points for the spline ranging from min(X) to max(X) instead of
using the actual data values as knot points.
The value of 50 can be changed by use of the !KNOTS k qualifier.
hence
datafile !knots 15
Y ~ mu X !r spl(X)
would form a spline on actual unique X values if there are less < 15 such
values;
otherwise the spline would be on 15 eqidistant knot points.
The former !SPLINE K qualifer has been redefined to
!SPLINE spl(X,k) <k explicit knot points>
where this !SPLINE statement MUST appear on the line immediately
after the data filename line and before the linear model line.
k is the explixit number of knot points and
<k explicit knot points> is the explicit set of knot points which the user
MUST supply. E.g.
datafile !knots 25
!SPLINE spl(X,9) 1 3 5 7 10 13 15 17 19
Y ~ mu X TREAT X.TREAT !r spl(X) TREAT.spl(X,9)
would form an overal spline on actual unique X values if there are less < 25
such values; otherwise the spline would be on 25 eqidistant knot points;
and an interaction spline component based on the 9 explicitly nominated
knot points. When supplying knot points, you must ensure they provide
reasonable coverage of the actual values in the variate.
If you want to force the spline to have a particular number of equidistant
knot points ranging min(X) to max(X), use the spl(X,k) notation without
a preceeding !SPLINE definition.
E.g.
datafile !knots 25
Y ~ mu X TREAT X.TREAT !r spl(X,8) TREAT.spl(X,8)
forms both spline components on 8 equidistant knot points
[!knots 25 is ignored in this example]
I trust you are all well.
Arthur
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Arthur Gilmour PhD mailto:Arthur.Gilmour@agric.nsw.gov.au
Principal Research Scientist (Biometrics) fax: <61> 2 6391 3899
NSW Agriculture <61> 2 6391 3922
Orange Agricultural Institute telephone work: <61> 2 6391 3815
Forest Rd, ORANGE, 2800, AUSTRALIA home: <61> 2 6362 0046
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While they watched, He was taken up,
and a cloud received Him out of their sight.
And while they looked steadfastly toward heaven as He went up,
behold two men stood by them in white apparel who also said
"Men of Galilee, why do you stand gazing up into heaven?
This same Jesus who was taken up from you into heaven,
will so come in like manner as you saw Him go into heaven."
Acts 1 9:11
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