Starting a few months ago, I believe, the StackExchange site software began adding an "impact" statistic to a user's profile. The impact statistic is posted in the upper-right portion of the screen that's shown when one clicks a user's profile. The impact is expressed as the number of people one has reached. For instance, TeX.SE currently estimates my impact at "~ 5.5 million people reached". Very flattering -- actually, perfectly mind-boggling!
Perusing the profiles of the 5 TeX.SE users who have more than 200k lifetime points at present, one finds impact estimates ranging from a high of 14.7 million people to a low of just [!] 6.4 million people. Among the 11 users whose lifetime total point count is currently between 100k and 200k, the impact estimates vary between 2.1 million and 9.3 million people reached. Among the 6 users with a current lifetime point count between 50k and 55k (a fairly tight band), the impact ranges from a low of 271k to a high of 2.9 million -- a ratio or more than 10:1!
Clearly, one's lifetime point count and the impact statistic are not exactly tightly linked. How does the site estimate/guesstimate the impact factor? What informational value does the impact estimate possess?