Time series data is a sequence of observations taken at specific time intervals. To understand it, we need to establish some key terms.
The current time is represented as t.
The observation made at the current time is represented as obs(t).
We often look at observations made at prior times, known as lag times or lags.
These are represented by negative numbers relative to the current time, e.g. t-1 for the previous time and t-2 for the time before that.
On the other hand, times in the future are represented by positive numbers relative to the current time, e.g. t+1 for the next time and t+2 for the time after that.
These are what we're interested in forecasting.
To make things simple, we often drop the obs(t) notation and use t+1 instead.
We also use shorthand such as a lag of 10 or lag=10 to refer to an observation at a lag.
📢 TL;DR
▶️ t-n represents a prior or lag time
▶️ t represents the current time and point of reference
▶️ t+n represents a future or forecast time
Understanding these standard terms is crucial for navigating time series data and making accurate predictions.
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Time Series Analysis and Time Series Forecasting are both methods used to analyze and make predictions about data collected over time, but they have different focuses and applications.
▶️ Time Series Analysis is the process of understanding the underlying structure and patterns in a dataset.
It is used to identify trends, patterns, and relationships in the data, as well as to examine the behavior of a variable over time.
Walmart has been using time series forecasting for decades to predict sales and optimise inventory levels.
By analysing historical sales data, weather patterns, and other factors, they're able to make more accurate predictions about future demand for products.
This allows them to ensure they have the right products in stock at the right time, reducing stockouts and increasing customer satisfaction.