12 Introduction
A sequence of data points organized in time order
A univariate time series is a sequence of measurements of the same variable collected over time. Most often, the measurements are made at regular time intervals.
- One difference from standard linear regression is that the data are not necessarily independent and not necessarily identically distributed.
- One defining characteristic of a time series is that it is a list of observations where the ordering matters.
- Ordering is very important because there is dependency and changing the order could change the meaning of the data.
Time-series data is common across many industries.
- Finance: stock prices, asset prices, macroeconomic factors
- E-Commerce: page views, new users, searches
- Business: transactions, revenue, inventory levels