I found recent data on the Appalachian Trail Conservancy's "2000 Milers" page, massaged it a bit in a spreadsheet, and came up with both annual completion rates, and average drop-out rates by milestone for the period covering 2005-2011 ...
|Miles Fm||Completion||Drop Out|
|Springer Mountain, GA||0||1392||1150||1125||1250||1425||1460||1700|
|Neels Gap, GA||30||1156||1076||1005||1150||1325||n/a||n/a||90%||10%|
|Fontana Dam, NC||160||1124||n/a||n/a||1050||911||n/a||n/a||76%||24%|
|Harpers Ferry, WV||1000||682||659||613||667||709||747||849||52%||48%|
|Mt. Katahdin, ME||2100||367||354||318||361||393||426||414||28%||72%|
The spreadsheet I used to derive this data is [here]. Some of the totals for milestones were missing from the ATC data set. So the average completions are based upon the totals of those who reach any given milestone over the period, and the total starts for only those years for which there is data for the milestone. Clear as mud?
I had read in multiple sources that the dropout rate at Neels Gap was closer to 15-20%, but that appears to have improved somewhat dramatically. The percentage of those who finish is also routinely stated as 20%, and the data shows it now to be significantly higher at 28%.
Still intimidating ...
Update (3/11/12) - In a post I started on this subject on WhiteBlaze, a representative of ATC provided background on how these estimates are derived:
For the record, here's some info from ATC:
Thru-hikers represent 80% of 2,000-milers. Section-hikers are the minority.
In recent years, we have arrived at our Springer northbound thru-hiker start numbers by analyzing the Amicalola Falls State Park thru-hiker register (which usually represents about 50-55% of starters--keep in mind some sign in there but go on the Springer to start) and the data collected by the Springer caretaker/ridgerunner. We know the Springer ridgerunner captures only a percentage, and he's only there 10 days out of 14 for part of the season. Since we've had both these sources available to us, we do not rely much on numbers from Neels Gap. But, Neels Gap was, for many years, the best source of info for us, and may again be someday if the situations change again on Springer or AFSP.
In 2011, we estimated that 1700 northbound thru-hikers started at Springer. Of those, 54% signed in at Amicalola Falls. 910 prospective thru-hikers signed in at Amicalola Falls. If the 54/46% Amicalola/Springer split is also representative of those who did not report completions, that would tell us that 1685 northbounders started. Seems to me the 1700 count is pretty darn close.
In addition to the Springer caretaker (Jonathan Lemberg), the following entities and individuals make our thru-hiker stats possible: the Georgia A.T. Club, the U.S.F.S., Amicalola Falls State Park (Ron Brown in particular), ATC HQ volunteer Greg Stover, and ATC staff and volunteers here at HQ and in our Asheville, NC office (Andrew Downs). ATC currently funds the Springer caretaker/ridgerunner position.
A final note: we base our northbound completion numbers on the 2,000-miler reports we receive, not the numbers from Baxter. Baxter northbound thru-hiker numbers are typically almost 50% higher than ours.
If I understand that last para correctly, it implies that thru-hikers reporting completion at Baxter could have been as high as 616 for a 37% completion rate in 2011 - And that's with a hurricane that tore up the northeast!