Non-Stationary Time Series

A non-stationary time series is a sequence of data points collected over time where the statistical properties, like the mean and variance, change. This could be due to trends (like increasing sales over years), seasonality (sales peaking during holidays), or other factors that cause fluctuations. In contrast, a stationary time series maintains constant properties throughout its duration. Non-stationary data is important because it often requires special analysis techniques to understand underlying patterns and make predictions, as traditional methods might not work effectively with data that changes behavior over time.