Showing the rise and decay of topics over the last two months (= default setting, which can be changed using the date selector), the trend chart provides the following time series:

• Frequency (Total, Positive and Negative). The displayed frequency values represent the number of occurrences in the last seven days. Selecting positive or negative coverage through the global sentiment filter affects the data displayed in the chart. Once activated, the footer of the portal also shows the current filter status.
• Sentiment (Mean). This time series shows the average sentiment towards the selected topic for the selected source and interval.
• Disagreement (Standard Deviation of Sentiment): The standard deviation of the sentiment distribution reflects how contested a particular topic is (the term ‘oil spill’, for example, tends to have a low standard deviation since everyone agrees on its negative connotation).

Display Features. The vertical axis is rescaled automatically, a feature that is particularly useful if one keyword dominates the coverage and therefore obscures the distributions of the other keywords. Hovering above a data point displays the associated keywords and daily statistics (frequency, mean and standard deviation of sentiment). This mouse-over effect identifies topical trends and shows their impact on the individual peaks in the chart. Clicking on a data point triggers a search for this particular topic cluster in the preceding week.