The statistical picture is difficult to understand.

On the one hand, the Packers gave up 4,796 net passing yards in 2011, most in NFL history. On the other, the Packers intercepted 31 passes, tops in the league.

The first number suggests the Packers struggled in coverage. The second suggests they were covering pretty tight at least a fair amount of the time, even without safety Nick Collins for all but the first two games.

The truth, as usual, lies somewhere in between. The secondary isn’t solely responsible for all those passing yards, not when the team’s sack total dropped from 47 to 29, forcing the defensive backs to cover receivers longer. But the unit isn’t free of blame, either, not when Green Bay’s high-scoring offense forced opponents into catch-up mode. Knowing the other teams were going to pass should have made them easier to stop.

One theory is that the corners and safeties took a lot of chances, which helped produce 25 of the team’s 31 interceptions (linebackers had the other six) but also led to surrendering more big plays. Another theory is that seeing holes in the coverages, the quarterbacks were taking more chances and willing to live with a few mistakes along the way to a big yardage day.

Either way, the Packers didn’t anticipate opponents having that much success throwing the ball against them in 2011, and they’ll be looking for ways to change that in 2012.

Cornerbacks—There’s a lot to like in a top three of Tramon Williams, Charles Woodson and Sam Shields, but there are some questions heading into 2012.

How much was Williams affected by that shoulder injury he sustained in Week 1? He didn’t look like the same player he was in 2010, but he wasn’t as healthy, either. A full-strength Williams will be expected to return to his 2010 form.

Is Woodson going to move to safety? It’s not out of the question, but he plays such a hybrid position in Dom Capers’ defense that whether he’s listed as a corner or safety might be only a matter of terminology. Woodson is at his best when he’s hovering around the line of scrimmage, able to blitz, attack against the run or cover a slot guy. Call it whatever position you want, but Woodson still led the secondary with seven interceptions and two sacks in 2011, and was second to Williams with 20 passes defensed.

How will Sam Shields look after a full offseason program? Shields looked like a rising star at the end of his rookie season but may have been hurt by the lockout as much as any player. Issues arose with his tackling. The Packers under Mike McCarthy take a lot of pride in their offseason program, and Shields should reap some benefits in 2012.

As for the depth, injuries in training camp derailed fourth-round draft pick Davon House’s season. He missed too much practice time and couldn’t catch up, though he’ll get a clean slate to display and develop his talent in his second season. Jarrett Bush and Pat Lee are free agents, so it’s unknown whether either or both will be back, and Brandian Ross spent his entire rookie season on the practice squad.

Safeties—The key issue here is whether or not Collins will return. He’s supposed to find out in March if he can resume his career after a Week 2 injury that required neck surgery. That decision, which Collins has said he’s leaving up to his doctors, will chart the Packers’ course at this position.

Morgan Burnett’s second season, as expected, was up and down. He only played in four games as a rookie and was coming back from reconstructive knee surgery. Then, beginning in Week 3, he didn’t have the Pro Bowler Collins next to him anymore. This will be the year the biggest strides will be expected from Burnett, now that he has a full, healthy season under his belt.

Top backup Charlie Peprah, by his own admission, didn’t play as well as an injury replacement in 2011 (for Collins) as he did in 2010 (for Burnett), another indication of the impact of Collins’ loss. Peprah did rank second on the team with five interceptions, but his season was a lot like many in this unit – he made some big plays, and gave up some, too.

Undrafted rookie M.D. Jennings got most of his playing time on special teams and could be another player ready to make a jump with an offseason program on the horizon. Anthony Levine was perhaps headed for a roster spot last summer before a concussion relegated him to the practice squad for a second straight year.

Summary—In the pass-oriented NFL, no team ever has enough corners, so look for the Packers to fortify this position even with the up-and-coming House looking to emerge. If either Bush or Lee isn’t back, multiple additions are a must, and that may be the case in any event. General Manager Ted Thompson has selected a cornerback in all but two of his Green Bay drafts, and in those years he didn’t, he added a veteran free agent (Frank Walker, 2007) and a key undrafted rookie (Shields, 2010). Safety could be an offseason priority, regardless of Collins’ decision, because even if he does come back, the Packers may want insurance in the form of greater depth. Collins’ return would be welcomed and seen as a big boost, but recovery from a career-threatening injury is never guaranteed.

Position by position series: Linebackers