Basic Concepts

Time series arise in many different contexts including minute-by-minute stock prices, hourly temperatures at a weather station, daily numbers of arrivals at a medical clinic, weekly sales of a product, monthly unemployment figures for a region, quarterly imports of a country, and annual turnover of a company. That is, time series arise whenever something is observed over time. While a time series may be observed either continuously or at discrete times, the focus of this book is on discrete time series that are observed at regular intervals over time.