Under general conditions the sample covariance matrix of a vector martingale and its differences converges weakly to the matrix stochastic integral from zero to one of BdB; where B is vector Brownian motion. For strictly stationary and ergodic sequences, rather than martingale differences, a similar result obtains. In this case, the limit is the same with a constant matrix, of bias terms whose magnitude depends on the serial correlation properties of the sequence. This note gives a simple proof of the result using martingale approximations.
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Length: 9 pages Date of creation: Jul 1987 Date of revision: Publication status: Published in Econometric Theory (1988), 4: 528-533 Handle: RePEc:cwl:cwldpp:846
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