Definition
WordPress plugin rank stability is the share of plugins that moved up, down, or held the same popularity rank between two dates. It is stated along with the median number of places moved by plugins that did move. It describes reshuffling inside the ranked set over the period, not any single plugin's own path. All three shares are drawn from the same starting group.
Population and window
Rivale measures rank stability across the top 12,500 plugins. The window compares the last day of the report month against the last day of the previous month. This gives a one-month span between the two rank readings. Rank on each date is taken from WordPress.org's own popularity ordering.
How it is computed
Each plugin's rank on the later date is compared with its rank on the earlier one. A plugin moves up when its rank number falls. The median move is the middle value of the number of places moved, ignoring direction, within each rank group. Some plugins leave the top 12,500 during the month. They have no rank to compare on the later date, so they count as neither up, down nor unchanged, and the three counts add up to less than the whole group.
How to read it
A plugin moves up when its rank number falls. A lower rank number means a more popular plugin under WordPress.org's own ordering. The median move is taken within each popularity rank and ignores direction. It counts only how many places were moved, not which direction. Read it beside departures from the top 12,500 plugins. Plugins that left the set during the month have no later rank to compare, so they are excluded from all three counts. Reading the median move alongside the up and down shares shows how many plugins moved and roughly how far.
What it is not
Rank stability does not include plugins that left the top 12,500 plugins during the month. The three shares stated together do not add up to the whole starting group. It does not state an exact rank for any plugin at either date. It does not measure download or install change directly, only movement in rank position. It is not a measure of why a plugin's rank moved, only of how much it moved.
Related measures
Departures from the top 12,500, Entries into the top 12,500, Download change