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Dynamic modell<strong>in</strong>g <strong>of</strong> large-dimensional covariance matrices 301<br />

implied by it. Substitut<strong>in</strong>g σ (RC)<br />

ij for sij <strong>in</strong> Eq. (7) and multiply<strong>in</strong>g by M gives for<br />

the optimal shr<strong>in</strong>kage <strong>in</strong>tensity:<br />

Mα ∗ =<br />

�Ni=1 � � �√Mσ � �<br />

Nj=1<br />

(RC) √Mfij, Var ij − Cov<br />

√ Mσ (RC)<br />

��<br />

ij<br />

�Ni=1 � � �<br />

Nj=1<br />

Var fij − σ (RC)<br />

�<br />

ij + (φij − σij) 2<br />

� . (20)<br />

Note that this equation resembles expression (8). The only difference is the scal<strong>in</strong>g<br />

by √ M <strong>in</strong>stead <strong>of</strong> √ T , which is due to the √ M convergence. In this case πt,<br />

the first summand <strong>in</strong> the numerator, is simply the sum <strong>of</strong> all diagonal elements <strong>of</strong><br />

�t. By us<strong>in</strong>g the def<strong>in</strong>ition <strong>of</strong> the equicorrelated matrix, it can be shown that the<br />

second term, ρt, can be written as (suppress<strong>in</strong>g the <strong>in</strong>dex t)<br />

ρ =<br />

N� �√ �<br />

(RC)<br />

AVar Mσ ii<br />

i=1<br />

+<br />

N�<br />

N�<br />

i=1 j=1,j�=i<br />

�<br />

√M �<br />

ACov ¯r σ (RC)<br />

ii σ (RC)<br />

jj , √ Mσ (RC)<br />

�<br />

ij . (21)<br />

Apply<strong>in</strong>g the delta method the second term can be expressed as 5<br />

¯r<br />

2<br />

⎛�<br />

�<br />

⎜<br />

�<br />

�<br />

⎝<br />

σ (RC)<br />

jj<br />

σ (RC)<br />

ii<br />

�<br />

�<br />

�<br />

+ �<br />

σ (RC)<br />

ii<br />

σ (RC)<br />

jj<br />

�√ (RC)<br />

ACov Mσ ii , √ Mσ (RC)<br />

�<br />

ij<br />

�√ (RC)<br />

ACov Mσ jj , √ Mσ (RC)<br />

�<br />

ij<br />

⎞<br />

⎠ .<br />

From this expression we see that ρ also <strong>in</strong>volves summ<strong>in</strong>g properly scaled terms<br />

<strong>of</strong> the � matrix. In the denom<strong>in</strong>ator <strong>of</strong> Eq. (20), the first term is <strong>of</strong> order O(1/M),<br />

and the second one is consistently estimated by ˆν = �N � �<br />

Nj=1<br />

i=1 fij − σ (RC)<br />

�2 ij .<br />

S<strong>in</strong>ce we have a consistent estimator for �, we can now also estimate π and<br />

ρ. In particular, we have<br />

ˆπ =<br />

ˆρ =<br />

N�<br />

N�<br />

i=1 j=1<br />

N�<br />

i=1<br />

hij,ij<br />

hii,ii + ¯r<br />

2<br />

5 cf. Ledoit and Wolf (2004).<br />

N�<br />

�<br />

N�<br />

�<br />

�<br />

�<br />

i=1 j=1<br />

(RC)<br />

σ jj<br />

σ (RC)<br />

hii,ij +<br />

ii<br />

�<br />

�<br />

�<br />

�<br />

(RC)<br />

σ ii<br />

σ (RC)<br />

hjj,ij,<br />

jj

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