Definition
WordPress plugin download change compares a plugin's downloads in the report month with its downloads in the month before it. It is stated per plugin, not as one directory-wide total. Each plugin carries its own figure for the month. The figure is a ratio between the two months, not a raw download count.
Population and window
Rivale measures download change across the top 12,500 plugins. Issue 1 compared four full weeks. Later issues compare full calendar months, per day, because months differ in length. Both date ranges are stated beside the figure in every issue.
How it is computed
Downloads in the report month divided by downloads in the previous month, per plugin. Plugins without measurable downloads in both months are excluded, and the count of plugins measured is stated with the figure.
How to read it
Download change reflects both new installs and update downloads drawn from the existing install base. A release in either month can move the figure. It can do this without any real change in how many people use the plugin. Read it beside update rate and updates and download change for the same plugins. That shows whether a release coincided with the move. A release itself generates downloads from the base that already had the plugin installed. Reading a single plugin's figure beside download volume for the same weeks also shows whether the move was large for that plugin.
What it is not
Download change is not a measure of active installs gained or lost over the two months. It does not isolate first-time downloads from update downloads. A plugin without measurable downloads in both months is excluded from the figure. The count of plugins actually measured is stated alongside the figure. It is not a lifetime download total, only a comparison of two adjacent periods.