[R] Do YOU know an equation for splines (ns)?

[Bert Gunter]

Does
?predict.ns
not do what you want without having to explicitly manipulate the spline basis?

-- Bert

On Tue, Jun 5, 2012 at 1:56 PM, Ranae <ranae.dietzel at gmail.com> wrote:
> Hi,
>
> I am looking at the change in N concentration in plant roots over 4 time
> points and I have fit a spline to the data using ns and lme:
>
> fit10 <- lme( N~ns(day, 3), data = rcn10G)
>
> I may want to adjust the model a little bit, but for now, let's assume it's
> good.  I get output for the fixed effects:
>
> Fixed: N ~ ns(day, 3)
> (Intercept) ns(day, 3)1 ns(day, 3)2 ns(day, 3)3
>  1.15676524  0.14509171  0.04459627  0.09334428
>
> and coefficients for each experimental unit in my experiment:
>
>   (Intercept) ns(day, 3)1 ns(day, 3)2 ns(day, 3)3
> 24    1.050360 -0.42666159 -0.56290877 -0.10714407
> 13    1.104464 -0.30825350 -0.53311653 -0.05558150
> 31    1.147878 -0.14548512 -0.78673906 -0.07231781
> 46    1.177781 -0.22278380 -0.80278177 -0.02321460
> 15    1.144215 -0.04484519 -0.06084798  0.07633663
> 32    1.213007  0.00741061  0.03896933  0.15325849
> 23    1.274615  0.16477514  0.00872224  0.23128320
> 41    1.215626  0.57050767  0.11415467  0.10608867
> 43    1.134203  0.48070741  0.72112899  0.18108193
> 12    1.091422  0.39563632  1.01521528  0.22597459
> 21    1.100631  0.44589314  0.98526322  0.23535739
> 35    1.226980  0.82419937  0.39809568  0.16900841
>
> NOW, I want to write a spline function where I can incorporate these
> coefficients to get the predicted N concentration value for each day.
> However, I am having trouble finding the right spline equation, since there
> are many forms on the internets.
>
> I know it won't be a simple one, but can some one direct me to the equation
> that would be best to use for ns?
>
> Thanks a lot,
>
> Ranae
>
>
> --
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>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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