Dear list members,
I need some advices with the specification of the Random Effects in
my Mixed model.
I got Panel data from 500 (i) district nested in 50 (j) towns over
10 (t) years.
There are 3 ex-ante known regimes (r) that are district specific and
vary with t. So every district is in regime 1 or 2 or 3 and that
might change over
time. I know a priori in which regime the districts are at time point t.
My goal is to analyse asymetric impacts of covariates X on y. y is
growth of Output. I apply a simple dummy specification, which uses
regime 1 as reference.
I estimated a mixed model via MCMCglmm (pooled mixed model):
prior_1 <- list(R = list(V = 1, nu=0.002), G = list(G1 = list(V =
diag(1), nu = 0.002)))
model1 <- MCMCglmm(y~ int + D2:int + D3:int + X + D2:X + D3:X
,random=~town,prior=prior_1)
int = intercept
D2 and D3 are dummy-variables indicating that district i is in regime 2 or 3
The random intercept for towns controls for the town specific
impacts on growth of districts. But in the specification above, only
"int" posseses a random intercept. So only the town specific impact
on growth in the reference regime 1 is captured by the random
intercept. If i assume that the town specific influence is different
between the 3 regimes, can I fit the model as:
prior_2 <- list(R = list(V = 1, nu=0.002), G = list(G1 = list(V =
diag(1), nu = 0.002),G2 = list(V = diag(1), nu = 0.002),G3 = list(V
= diag(1), nu = 0.002)))))
model2 <- MCMCglmm(y~ int + D2:int + D3:int + X + D2:X + D3:X
,random=~town + D2:town + D3:town, prior=prior_2)
Or are there better solutions to take care of the different town
specific influence on district growth during the 3 regimes?
Alternatively:
prior_3 <- list(R = list(V = 1, nu=0.002), G = list(G1 = list(V =
diag(3), nu = 0.002)))
model3 <- MCMCglmm(y~ int + D2:int + D3:int + X + D2:X + D3:X
,random=~ idh(as.factor(regime)):town, prior=prior_3)
This time the Random Effects are correlated, which is not the case
in model2, right?
Thanks in advance,
Linus Holtermann
Hamburgisches WeltWirtschaftsInstitut gemeinn?tzige GmbH (HWWI)
Heimhuder Stra?e 71
20148 Hamburg
Tel +49-(0)40-340576-336
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Email: holtermann at hwwi.org
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