The devil, of course, is in the details. For instance, NATO does not count attempted bombings, only those that explode. On the other hand, the UN has a very incomplete set of data since they are far less present around Afghanistan than NATO. The UN also counts crime, not just insurgency, although it may not make a difference to an Afghan if he is hurt or killed by folks who are merely greedy or are seeking a Taliban victory.
And that gets to a larger problem of perceptions. Even if violence is declining, Afghans do not perceive it as such. They may have the same kinds of misperceptions of Americans and Canadians who think there is more crime when the stats are actually down. The challenge here is that in Afghanistan, such a set of views is far more damaging since the fight really is over the competency of the government and potential substitutes (Taliban).
To say that things are going well on the battlefield is also always a very limited kind of claim in a counter-insurgency. Is the government providing effective services? Is it seen as legitimate or rapacious?
O'Hanlon provides some chillingly low expectations:
But also consider, Afghanistan is not that violent by the standards of war-torn — or even high-crime — countries. For example, whatever database is used, its monthly violence rates are roughly a tenth that of Iraq in the horrible years of 2004-2007; and perhaps a fifth of a country like Colombia today.