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I have been trying to estimate state space models using dlm package in R. The problem is that the model I am estimating requires inclusion of a few exogenous variables. I still can't figure out how to do it. Does any one know how to add exogenous variables to a state space model in dlm package?

AmateurRuser
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2 Answers2

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You almost certainly want to do this with a wrapper function and function pointers.

data(endogenous);
data(exogenous);
model <- function(en, ex) {
   # do stuff
   ...
}
# Now you can't call dlm on model because it expects a function of the form f(x)
# so you need to create one of that format
f <- function(x) {
   return( model(x,exogenous) );
}
out <- dlmMLE(endogenous, rep(0,6), f);

The second function (f) is basically a wrapper for your model in the correct form.

Mimshot
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Most probably those exogeneous variables will take known values which are multiplied by elements of the state vector. Then, you can make them time-varying elements of the observation matrix. There is a utility function which does almost all the work for you: dlmModReg. Type example(dlmModReg) to see how it constructs a state-space model with two "regressors". Also, have a look at the book Dynamic Linear Models with R if you can get hold of a copy.

If you provide a concrete example of model that you want to fit, we might help some more.

F. Tusell
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  • Actually I am trying to replicate Labauch and Williams (2003) paper on natural interest rate. It involves estimation in 3 stages, each stage requires inclusion of exogenous variables. Say: Measurement equations: $y_t = y_t^* + \alpha_1 (y_{t-1} - y_{t-1}^*)-\alpha_2 (r_{t-1} - r_{t-1}^*) + e_{1t}$, $\pi_t = \beta_1 \pi_{t-1} + b_y (y_t - y_{t-1}^*)+b_f (\pi_{t-1}^o-\pi_{t-1})+e_{2t}$ State equations: $r_t^* =c g_t +z_t, g_t =g_{t-1} +e_{5t}, y_t^* =y_{t-1}^* +g_{t-1}+e_{4t}, z_t = \gamma_1 z_{t-1} + e_{3t}$ For now only measurement equations have exogenous variables ($\pi_{t-1}^o$). – AmateurRuser Dec 09 '12 at 16:49