The Detroit Lions have been one of the surprises of the NFL this season. The franchise that hasn’t won a playoff game since after the 1991 season, or a division title since 1993, has looked like one of the league’s better -- and more consistent -- teams through the first month.

After four games, the Lions are tied with five other teams, including Green Bay, for the best record in the NFC at 3-1. How can one explain Detroit’s strong start? Is it something that can be sustained throughout the rest of the season? A guide through some numbers can help foretell Detroit’s future.

The defense is the reason for the Lions' wins. Their takeaways and their run defense have the Lions on pace for a defensive expected points added number of 37.85 -- second best in the league behind only Jacksonville.

The offense, though, has not been nearly as efficient. The Lions’ offensive EPA number of minus-20.07 is seventh worst in the league. They are the only team above .500 in the bottom 10 of the NFL in the statistic.

Lions cornerback Darius Slay is chased by the Falcons' offense after he intercepted a pass in Week 3. AP Photo/Rick Osentoski

Since 2010 only five teams have finished with an over-.500 record and made the playoffs with a bottom-10 offensive EPA: the Texans and Giants in 2016, the Broncos and Texans in 2015 and the Bears in 2010.

All five of those teams had defensive EPAs in the top six in the league that season, so at this point, if the Lions are going to make the playoffs, it’ll be off this type of model.

The defense has clearly been playoff-caliber. While yardage numbers allowed have been high, that’s a misnomer of a statistic because yards don’t always lead to points. In the statistics that matter, the Lions have been a top-10 unit. The Lions' defense has allowed 70 points -- tied with Sunday’s opponent, Carolina, for the sixth-fewest points allowed.

Detroit is holding teams to 86.3 yards per game rushing, seventh in the league. The yards per rush of 4.01 is higher than the Lions would like and could be a concern if Detroit ends up trailing in the fourth quarter against good teams.

The 41.8 QBR rating for opposing quarterbacks is sixth in the league and best in the division. Detroit has kept opponents from passing efficiently -- a major improvement from last season’s NFL-record completion percentage allowed. If you’re looking for a reason for Detroit’s start, opposing quarterback play is a big one.

So, too, are turnovers, as the Lions are intercepting 4.8 percent of opponent’s passes -- second in the league. The secondary has played like one of the best units in the NFL with two potential Pro Bowlers in cornerback Darius Slay and perennially underrated safety Glover Quin.

“We certainly think our guys have worked at it, we try to point those things out,” Lions coach Jim Caldwell said. “How we practice obviously makes a difference, but we’ve practiced them in years past as well, and hadn’t gotten nearly as many.

“But I do think that we got guys that are closing in on the ball a lot faster, guys are in better position when balls are loose. We got a lot of guys hustling to the ball, so the law of averages tells us we’re going to have a really good chance of getting our hands on it.”

The Lions' 10 sacks are tied for 14th in the league and their sack percentage of 6.9 percent is 21st in the league. Neither ranks particularly high, but they are better than a year ago and don’t include quarterback pressures. The disruptions the Lions have caused to opposing offenses have been critical to their success. Detroit has held teams to 15.75 offensive points scored per game, the third-lowest total in the league, trailing only Buffalo and Pittsburgh. The Lions’ points margin of plus-29 is fifth best in the league.

While the offense has struggled, there are signs of potential improvement.

The Lions are tied for ninth in red zone efficiency at 60 percent. They are also controlling games with the fifth-best time of possession in the league (32:39). More important, they aren’t turning the ball over. Matthew Stafford is being intercepted on fewer than 1 percent of his pass attempts (0.7), fifth in the league.

Detroit needs to keep both of those numbers high to have a chance to make the playoffs this season. The Lions sit at No. 19 in the league in three major categories: rushing yards per game (97.0), passing yards per game (202.8) and offensive points scored per game (19.5).

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The Lions’ third-down efficiency of 36.8 percent is No. 23 in the league -- second lowest among teams over .500 (the Steelers are at 36.5 percent). Detroit must find ways to stay on the field, otherwise its defense will eventually tire out. That would be a problem in playoff-potential games toward the end of the season.

The Lions saw a glimmer of hope Sunday against an aggressive Minnesota defense. They might have found a potent running back in Ameer Abdullah, and if he can push forward on first downs, it’ll make everything easier for the offense to convert shorter third downs.

“When you’re looking up and it’s second-and-13 in this league, it’s really difficult. When teams know that you have to gain a lot of yards with your next two snaps, it gets really difficult,” offensive coordinator Jim Bob Cooter said last week. “And I don’t think on first-and-10 we’ve been as good as we want to be, run game or pass game. We haven’t been necessarily as efficient in either manner.

“So, to me the key is first-and-10. Are you looking at a second-and-5 on the scoreboard after that or are you looking at a second-and-9, second-and-11, something like that? We would prefer the first option.”

The Lions don’t have many other options. The numbers show if the offense doesn’t improve, reaching the playoffs could be harder than anticipated.