Other or unknown

Hold an open slot for a cause you have not thought of. The named rivals may all be wrong, so treat your list as provisional and decide in advance what result would tell you something outside the list is driving things.

Hold an open slot for a cause you have not thought of. The named rivals may all be wrong, so treat your list as provisional and decide in advance what result would tell you something outside the list is driving things.

Example

You list algorithm change, price increase, competitor, and stockout for the 30 percent sales drop. You add: something unnamed. If sales stay flat after restocking, repricing, and confirming search rank held, you go hunting for a cause nobody in the forum mentioned.