An app says it has ten million accounts and two million active users.
Is there a way to see the real number?
I look at the app and see 182 people are posting right now. During the day, the number varies between 200 to 350 users at any one time.
If there are ten million accounts, 200 is not even 1%. The current users are 0.001%. Is that possible?
There’s a way to find out. The 1/9/90 Rule says that of the people in any activity (country music, skiing, surgery, etc.), 1% are the active creators; 9% are critics; 90% are passive observers. This has been well-studied in many fields by sociologists for 40-50 years. The actual numbers vary a bit: 1-3% for creators and 85-92% for observers, but in general, this ratio holds. (See Jakob Nielsen on Participation Inequality and Charles Arthur at The Guardian.)
If 200 postings are by the 1% active users, then there are 20,000 passive members. What if 200 postings are by 3% active users? Then the number of passive members is 6,700. So the number of active members is somewhere between 6,000 and 20,000 people, but not much greater (I seriously doubt it reaches 40,000).
This can be applied to just about any social app. Look at the number of actions (postings, videos, photos, music, game scores, etc.). Assume that’s 1% and you can calculate the number of passive users (oh, okay: multiply by 100).
Jakob Nielsen points out that the 1% are not representative of the group. It’s a mistake to take their postings or actions as representative.