The Numbers in Our Words: Words of Estimative Probability

Toward the end of this month I will almost cer­tainly post the tra­di­tion­al Lone Gun­man Year in Review post. Exactly how likely am I to do this? Am I able to quanti­fy the prob­ab­il­ity that I’ll do this? By using the phrase “almost cer­tainly”, I already have.

To provide unam­bigu­ous, quant­it­at­ive odds of an event occur­ring based solely on word choice, the “fath­er of intel­li­gence ana­lys­is”, Sher­man Kent, developed and defined the Words of Estim­at­ive Prob­ab­il­ity (WEPs): words and phrases we use to sug­gest prob­ab­il­ity and the actu­al numer­ic­al prob­ab­il­ity range to accom­pany each.

Kent’s idea has had a mixed recep­tion in the intel­li­gence com­munity and the dis­reg­ard­ing of the prac­tice has been blamed, in part, for the intel­li­gence fail­ings that lead to 9/11.

The words by decreas­ing prob­ab­il­ity:

  • Cer­tain: 100%
  • Almost Cer­tain: 93% ± 6%
  • Prob­able: 75% ± 12%
  • Chances About Even: 50% ± 10%
  • Prob­ably Not: 30% ± 10%
  • Almost Cer­tainly Not: 7% ± 5%
  • Impossible: 0%

The prac­tice has also gained some advoc­ates in medi­cine, with the fol­low­ing list of defin­i­tions formed:

  • Likely: Expec­ted to hap­pen to more than 50% of sub­jects
  • Fre­quent: Will prob­ably hap­pen to 10–50% of sub­jects
  • Occa­sion­al: Will hap­pen to 1–10% of sub­jects
  • Rare: Will hap­pen to less than 1% of sub­jects

It would be nice if there were such defin­i­tions for the many oth­er ambigu­ous words we use daily.