In the NFL, what is the difference between each of the designations for questionable vs doubtful? Which one is more severe?
In the NFL, there are injury designations. The injury designations indicate what percentage or chance that they'll play for that given day.
The NFL specifically has one that outlines them based on percentages:
Inactive (IA) - Players are officially inactive for the current game and will not play
Out (O) – Not scheduled to play
Doubtful (D) – Players have approximately a 25% chance of playing
Questionable (Q) – Players have approximately a 50% chance of playing
Probable (P) – Players are very likely to start in the upcoming week
The injury designations are exactly that; based on percentages. Additionally, from my experience they can change as the NFL week progresses: for better and worse.
Moreover, the Wall Street Journal has provided some insight regarding these injury designations as well:
"Probable" means definite. "Questionable" is closer to probable. And "doubtful?" If a player is listed as doubtful, like the Colts' Peyton Manning is this week, then there's virtually no doubt whatsoever that he's going to sit out.
In the NFL, teams are required to report injury statuses on a daily basis. Apparently, they shouldn't be taken literally:
It's long been known that injury reports aren't to be taken totally literally. The official NFL definitions are that "out" means a player definitely won't play that week; doubtful means at least 75% chance the player sits; questionable means 50-50 and probable means it's a virtual certainty he'll play. Indeed, the Patriots famously have listed quarterback Tom Brady as "probable" for years, even though he made 111 straight starts at one point.