Annotations are notes attached to dates that record in analytics what happened at a given time – the launch or end of a campaign, a website redesign, a price change, an outage, a change to tracking, a search engine algorithm update, or an unusual event in the industry. Their purpose is to make it possible, later on, to explain why a curve in a chart looks the way it does. Without this record, when evaluating results after several months, causes are guessed at and decisions are made based on assumptions. They can be kept directly in the analytics tool or in a simple table with a date, description and the author of the change. They are especially valuable for year-on-year comparisons, where without them nobody knows what was different in the compared period.
See also: Period comparison, Reporting cadence, Anomalies and Alerts.
