# Time Series Notes

**Topics:**Time series analysis, Regression analysis, Time series

**Pages:**3 (698 words)

**Published:**June 1, 2013

Main features of Time series Data

Observations have temporal ordering

Variables may have serial correlation, trends and seasonality Time series data are not a random sample because the observations in time series are collected from the same objects at different points in time For time series data, because MLR2 does not hold, the inference tools are valid under a set of strong assumptions (TS1-6) for finite samples While TS3-6 are often too restrictive, they can be relaxed for large samples. In essence, TS1, TS2, (z10), (h10) and (u10) are sufficient for large sample inference Serial correlation of a time series variable is the correlation between the variable at one point in time with the same variable at another point in time (z10), (h10), (u10)

z10 = E(ut | xt) = 0

When (z10) holds then the regressors are contemporaneously exogenous and OLS is consistent but is not sufficient for OLS to be unbiased When TS3 holds, which implies (z10), then the regressors are strictly exogenous and OLS is unbiased h10 = Var(ut | xt) = 2 and is known as contemporaneous homoskedasticity and is a weaker assumption than TS4 u10 = E(utus | xt,xs) = 0 and is a weaker assumption than TS5 FDL model and LRP

A FDL model allows the lags of one or more variables to affect the dependent variable The LRP is the impact on y of a permanent one unit shift in z at t Trends and Seasonality

Seasonal dummy variables can be used to account for seasonality with the first quarter as base and define three dummy variables Trends can be accounted for by adding a time trend in the model Estimate B1 and B2 by regressing yt, xt1, xt2 on the time trend and seasonal dummies and save the residuals respectively. Regressing the residual of yt on the two residuals of xt1 and xt2 without intercept. Further Issues with Time Series Data Summary Week 11

1. Asymptotic properties of OLS with time series

Theorem 11.1 (consistency)

Under TS1-2 and (z10), if {xt,yt} are...

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