This will produce a graph of the number of matches to your query over time.
You can access this by selecting the 'Frequency/Time' option in the 'Summary of Results' group in the 'Select a task..' drop down menu on the results screen. Some options to help you refine the graph will be displayed below the 'Select a task...' menu.
The options are:
Checking this option will modify the frequency of results to the frequency per million words. Unchecking it will use the raw frequency. The default is checked (frequency per million).
Checking this will include the trend analysis line on the graph, which shows the significance of a change in frequency. This also displays the seasonality score at the bottom of the graph. The default is unchecked.
The graph shows the frequency of results, plotted for each month, over time. The dashed green line shows the raw frequency value whilst the constant green line shows the moving average.
If you have chosen to plot the trend analysis then two red dashed lines will be displayed representing the bounds in which we would expect the trend to deviate. The trend is plotted in a constant red line and if this goes beyond the dashed red lines the change be said to be significant. This will not be plotted for the first few years because it requires some training data before being able to accurately assess the trend.
If you have plotted the trend analysis a seasonality score is displayed at the bottom of the graph. This represents how similar the frequency of results is for each month of each year. The lower the score the more seasonal they are.