Q4. Distinguish between weak stationarity and strong stationarity. Explain the methods of testing for stationarity in a univariate time series model.
- Weak stationarity: Constant mean, variance, and autocovariance depending only on lag.
- Strong stationarity: Joint probability distribution is time-invariant for all moments.
- Strong stationarity implies weak stationarity, but not vice-versa (unless Gaussian).
- Visual stationarity tests: Time series plots, ACF, and PACF behavior.
Answer: In advanced econometrics, understanding the stationarity of a time series is crucial for valid statistical inference and forecasting. Stationarity implies that the statistical properties of the series do not change over time. This concept is typically divided into two forms: weak stationarity and strong stationarity. Weak stationarity, also known as covariance stationarity, is a less restrictive form. A time series Yt is weakly stationary if it satisfies three conditions: its mean is constant o...