Update (5/7) - The Nats have locked in four more wins, but with three of those being one-run games, their pythagorean is separating a bit more from their actual record. Assuming they keep performing, a finish in the mid-to-upper 80s still seems resonable.
In a recent post on FanGraphs, Strong Starts Don't Mean That Much, Dave Cameron mentions a quick and dirty method of regressing a team's record to their true talent level by adding 35 wins and 35 losses to their current record. That will yield a team's expected winning percentage for the rest of the season which, when added to their current record, results in a very rough estimate of their final record. Below, I use this methodology to estimate the Nationals final 2012 record based first on their actual
14-8 18-10 start and then on their Pythagorean record of 13-9 16-12.
Estimated 2012 Nationals Record based on Current Record
Current Record: 18-10.
Add 35-35 for expected true talent winning pct.: .541 (53-45).
Multiply by 134 for expected record over remaining 134 games: 72.5-61.5.
Add to current record for final expected record: 90.5-71.5.
Round to nearest game: 91-71.
Estimated 2012 Nationals Record based on Pythagorean Record
Pythagorean Record: 16-12.
Add 35-35 for expected true talent winning pct.: .520 (51-47).
Multiply by 134 for expected record over remaining 134 games: 69.7-64.3.
Add to current record for final expected record: 85.7-76.3.
No rounding necessary: 86-76.
Average of the two methods: 88-74
Caveat: This method doesn't take into account injuries, innings limits, or any stats other than wins, losses, runs scored, and runs allowed.