Laws of Large Numbers for Dependent Heterogeneous Processes

Laws of large numbers (LLN's) for mixingale sequences are an essential tool in the proofs of consistency of estimators when dependent processes are considered. A mixingale sequence can be viewed as an asymptotic equivalent of a martingale difference sequence. In a recent paper, Andrews (1988) extended the mixingale concept and established weak LI -type LLN's for mixingales. Andrews' work extends the results of McLeish (1975), who introduced the mixingale condition. In Section 2 of this paper, Andrews' conditions for an LI -type LLN for Lp-mixingale sequences will be extended such as to cover the case of trended mixingale sequences. Recently, Hansen (1991, 1992) proved some new strong LLN's using Andrews' Lp-mixingale concept. Those results extend the results of McLeish. In Section 3 of this paper, the conditions of both McLeish and Hansen for a strong LLN to hold will be relaxed substantially for the important case of Lp-mixingales with uniformly bounded pth moments and bounded indices of magnitude. The results obtained in Section 3 are complementary to those obtained by Hansen and McLeish since our results will not be powerful in the case of increasing indices of magnitude or the case that no uniform moment bound exists. In Section 4, we apply our results to near epoch dependent sequences. Section 5 concludes this paper with the proofs of the theorems.