The challenge of replacing Welker

The Patriots are 5-0 all-time against the Ravens, including a win this season. Tom Brady is 8-0 at home in the postseason. The Patriots haven't lost a home playoff game since Pete Carroll was at the helm. So what's with the ominous cloud hovering over Foxborough?

Wes Welker's season-ending knee injury derailed any late-season momentum. Suddenly, there are more question marks heading into Sunday than there have been for any game since Week 2 of 2008.

Just how valuable was Welker?

Before diving into how to replace Wes, let's appreciate what he meant to the Patriots. While playing just a shade more than 13 games, Welker hauled in 123 passes, tying Herman Moore for second most in NFL history behind only Marvin Harrison's 143 in 2002. Despite 20 fewer catches, Welker's 2009 campaign was arguably more prolific than Harrison's. Ignoring his abbreviated one-catch performance in Week 17, Welker averaged 9.4 receptions in 13 games. Multiplied over a full 16 games, Welker would have 150 receptions at that rate.

Welker's season is impressive when looking at his receptions total. It's historic when you consider the rate at which he was catching balls before the injury. Now factor in how often he was targeted, and Wes Welker's season is downright baffling.

Welker was targeted 162 times, a high number, but only the third most in the NFL in 2009, and the 35th most in the past decade. However, he hauled in 75.9 percent of the passes thrown his way. In the six seasons in which a receiver caught 122 or more passes, Welker was targeted by far the fewest times and easily had the highest catch percentage.

In fact, over the past decade, Welker's 2009 catch percentage was the second highest among all 352 players targeted at least 100 times in a season. The only one higher? Welker's 77.2 percent in 2007. His 2008 season ranks third. In short, Welker's productivity, reliability and efficiency over the past three seasons are unprecedented. According to the Elias Sports Bureau, his three-year total of 346 receptions has only been topped by Marvin Harrison's 354 catches from 2000 to 2002.

Can Edelman impersonate Welker?

According the Elias Sports Bureau, the last time the NFL's receptions leader missed a playoff game was Mac Speedie of the 1952 Browns. Before him, it was Red Badgro of the 1934 Giants. Sadly, neither is known as the Wally Pipp of the NFL, so history may not work in the Patriots' favor here.

If you had to pick one guy to fill in for a record-setting receiver, a rookie seventh-round pick might not be your first choice. Throw in the fact he was a college quarterback, and the prospect seems even more alarming. A year ago, Julian Edelman wasn't even among the 330 college players invited to the NFL combine.

Yet, Edelman is the Patriots' best hope for doing an imitation of Welker, who himself went undrafted. In the three games missed by Welker, Edelman averaged seven receptions per game. That would put him on pace for 112 catches over a 16-game season. Only Welker himself had more than that this season.

Edelman hauled in 68.5 percent of the passes thrown his way, an impressive rate if not quite on Welker's level. That percentage -- like Welker's -- is helped by the frequency with which he is the target of short passes. However, while Welker only dropped five of the 162 passes thrown his way, Edelman has just one fewer drop despite 108 fewer targets. His drop rate is more than double Welker's.

Even if Edelman replicates Welker's statistics, past games indicate that the Patriots' offense will still miss Welker's presence. Tom Brady had a 102.9 passer rating and 68.0 completion percentage with Welker healthy. Without him, Brady's rating plummets to 68.9 and his completion percentage slips to 56.3. Not surprisingly, Brady targeted Randy Moss more without Welker in the lineup, and even less surprisingly, defenses keyed on Moss. Of his 30 targets with Welker injured, Moss caught only 12. That 40.0 catch percentage is down from 59.6 percent with Welker in the lineup.

So all Edelman has to do is replace one the most prolific pass-catchers in NFL history, keep opposing defenses honest enough to free up Randy Moss and overcome the pressures of playing his first playoff game.

Can the running game help to replace Welker?

Could the ultimate solution not be a wide receiver at all? While logic points to Edelman, the Patriots could look to the running game in Welker's absence.

When healthy, Welker has in some ways been used as a surrogate running back. First down? Rather than picking up 4 yards on the ground, let Welker create a second-and-short. Short yardage? Rather than punch it up the middle, why not sling it to Welker, who inevitably had inside position on the cornerback. Quick shots to Welker were the bread-and-butter of the Patriots' offense.

The Patriots were one of only eight teams -- and the only AFC team -- that had more pass attempts than rushes on first down. Welker was the target on first down 63 times and had 52 receptions, most in the NFL.

He was also king of the quick-strike reception. His catches were an average of 5.0 yards from the line of scrimmage. For some perspective, Randy Moss' average catch was 11.2 yards downfield. Of the 47 wide receivers who caught 50 or more passes this season, no one's average yards at catch were lower than Welker's.

Welker was targeted behind the line of scrimmage 30 times. That ranks just 17th in the NFL. However, of the 16 players ahead of him on that list, 15 are running backs, with Miami's Davone Bess the lone exception.

So who might be the replacement in this aspect of the offense? Edelman is still the obvious answer. Of his 37 receptions, 12 came behind the line, as he was traditionally used in much the same way as Welker. But could the Patriots run the ball more without Welker?

Previous results on that are mixed. Including last week, when they had 19 rushes, the two games in which the Patriots had the fewest rushing attempts both came with Welker injured. However, the Patriots did turn to the run when Welker missed the Falcons game (39 rushes for 168 yards). In that game, the Patriots held nearly a two-to-one advantage in time of possession.

While some Patriots fans would love to see a renewed commitment to the run, most signs point the other way.

Bill Belichick seems to have soured on Laurence Maroney, who lost four fumbles in seven games before taking a seat early in the Jaguars game. Fred Taylor and Sammy Morris could be asked to carry the load, but they have one 20-carry game between them this season.

More significantly, the Ravens' rush defense is among the best in the business. They led the NFL in allowing only 3.4 yards per carry. Allowing only 93.3 rushing yards per game, Baltimore boasts the AFC's No. 2 rush defense. In their Week 4 win over the Ravens, the Patriots ran for only 85 yards on 30 carries, their worst yards per rush (2.8) all season.

Indeed, the best way to beat the Ravens appears to be through the passing game. In their nine wins, the Ravens have allowed only 183.8 yards per game through the air, a number that is hugely inflated by a 436-yard performance by Philip Rivers. However, in their seven losses, the Ravens have allowed 264.6 passing yards per game.

Jeremy Lundblad is a researcher with ESPN Stats & Information. He provides statistical analysis for ESPNBoston.com.