Read his arguments. He does NOT concede that he is wrong. In fact he insists he was right.
Krugman observes that after the original stimulus:
* Interest rates DID NOT rise as many feared. He argued that the stimulus was too small. Temporary deficits werent a problem as long as the economy remained depressed; we were awash in savings with nowhere to go.
* Inflation did not rise as many feared. Key measures of inflation have fallen from more than 2 percent before the economic crisis to 1 percent or less now, and Japanese-style deflation is looking like a real possibility.
* GDP Growth DID accelerate last year, as the stimulus reached its predicted peak impact, but has fallen off just as some of us feared as the stimulus has faded.
IN OTHER WORDS, THE STIMULUS WORKED, BUT IT DID NOT WORK BECAUSE IT WAS NOT APPLIED IN A SUFFICIENT SCALE !!!
ERGO : WE NEED ANOTHER ROUND. A BIGGER ONE AT THAT !!
Thats this Nobel Economics Laureates take.
Also, Krugman has lectured that you CANNOT compare a trillion dollar economy to a household budget. That is trying to compare apples with oranges. They are two different things, both in scale and in scope ( not saying I agree with him, just paraphrasing his arguments ).
And just because inflation isn't back yet doesn't mean it won't be.