[R-SIG-Finance] Optimization of ARFIMA in rugarch - Quick question and context

[alexios ghalanos]

The returned list from autoarfima has 2 slots, 'fit' and 'rank.matrix'. 
The former is of class ARFIMAfit, and though not exported to work with 
it, you can use

 >rugarch:::.nyblomTest(fit).

If you provide some additional details (i.e. reproducible code and which 
data you are using...monthly/daily,value-weighted or equally weighted) 
then we might be able to provide some additional help.

Regards,

Alexios

On 02/12/2014 21:57, Nicholas Manganaro wrote:
> Question:
> Is there a way to query the Nyblom joint statistic result out of an ARFIMAfit class object, the way there is for a uGARCHfit class object?
>
> Context:
> I am running an analysis on subsets from 12 return time series from the Fama/French Factors files (source: http://mba.tuck.dartmouth.edu/pages/faculty/ken.french/data_library.html) which evidence skewed Student t distributions.
> I initially used autoarfima from the rugarch package using the nlminb solver, which generated results for some of the series, but not some others. I sequentially tried the other available solvers on the entire set of series to see if they would identify ARMA models for more of these sets.
> As I hope you can see in the table below the results were mixed. Some observations:
> •	There was no solver that found ARMA coefficients for all sectors (not necessarily a problem);
> •	For many sectors, the values estimated for the orders of p and q for AR and MA varied across the solvers; and
> •	None of the solvers consistently provided either the lowest BIC or AIC score for the results across all sectors.
>
> 					Solver			
> 									
> 		nlminb		solnp		gosolnp	nloptr
> 		AR	MA	AR	MA	AR	MA	AR	MA
>          Manuf  	4	4	4	4	5	4	4	4
> 	Other  	NA	NA	NA	NA	0	1	0	1
> 	Money  NA	NA	NA	NA	NA	NA	NA	NA
> 	Chems  0	5	0	5	0	5	0	5
> 	NoDur  	NA	NA	NA	NA	NA	NA	NA	NA
> 	Shops  	NA	NA	NA	NA	3	4	NA	NA
> 	Durbl  	0	1	5	5	5	5	5	3
> 	BusEq  	5	3	5	3	5	3	5	2
> 	Hlth   	NA	NA	NA	NA	0	5	NA	NA
> 	Telcm  	5	0	5	5	5	5	5	0
> 	Utils  	3	4	3	4	0	5	3	4
> 	Enrgy  	0	1	5	3	4	3	5	3
> 	Mkt.RF 	5	3	3	2	NA	NA	NA	NA
>
>
> While I understand that the Nyblom test is an indicator of the stability of the results across a series, within the model results for a sector from the available solvers, a higher Nyblom joint statistic qualitatively seems to indicate higher quality test results across a number of tests, including the coefficient t statistics and the Ljung-Box results per sector. As a result, I was thinking I might use the Nyblom joint statistic as an indicator in automating the selection of the desired model from possible alternatives, but do not see how to query out that result for further testing as an indicator, although I can see it as part of the $fit object.
>
> Please let me know if there is either such a capability for the ARFIMAfit class that I may have overlooked, or a function I might call to generate the joint Nyblom statistic and critical values using the zoo time series data and the existing autoarfima results on hand.
>
> Thanks.
>
> -Nick
>
>
>
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