In the

United States Court of Appeals

For the Seventh Circuit ____________________

Nos. 15-2385 & 15-2386

KLEEN PRODUCTS LLC, et al.,

Plaintiffs-Appellees,

v.

INTERNATIONAL PAPER COMPANY, et al.,

Defendants-Appellants.

____________________

Appeals from the United States District Court for the

Northern District of Illinois, Eastern Division.

No. 10 C 5711 — Harry D. Leinenweber, Judge.

____________________

ARGUED DECEMBER 8, 2015 — DECIDED AUGUST 4, 2016

____________________

Before WOOD, Chief Judge, and BAUER and WILLIAMS, Circuit Judges.

WOOD, Chief Judge. The antitrust laws prohibit competing 

economic actors from colluding to agree on prices, either directly or through such mechanisms as output restrictions. See 

United States v. Socony-Vacuum Oil Co., 310 U.S. 150 (1940); 

Palmer v. BRG of Georgia, Inc., 498 U.S. 46 (1990). That is just 

what the plaintiffs in the case before us allege the producers 

and sellers of containerboard did. The plaintiff-purchasers 
2 Nos. 15-2385 & 15-2386

filed this suit under Sherman Act § 1, 15 U.S.C. § 1, seeking to 

recover treble damages for the overcharges they allegedly 

paid. See Clayton Act § 4, 15 U.S.C. § 15. What brings the case 

before us at this time—well before the merits have been resolved—is the district court’s decision to certify a nationwide 

class of purchasers under Federal Rule of Civil Procedure 23. 

The defendants, International Paper Company, Georgia-Pacific LLC, Temple-Inland Inc., RockTenn CP, LLC, and Weyerhauser Company (to whom we will refer collectively as Defendants unless the context requires otherwise), asked us to 

accept this interlocutory appeal from the certification decision 

pursuant to Rule 23(f). We agreed to do so. Finding no abuse 

of discretion in the district court’s decision, however, we affirm.

I

The Purchasers allege in their complaint that the defendant companies agreed “to restrict the supply of containerboard by cutting capacity, slowing back production, taking 

downtime, idling plants, and tightly restricting inventory.” 

These actions predictably led to an increase in the price of containerboard—a price increase that caused Purchasers to pay 

more for containerboard products than they would have paid 

in the absence of the illegal agreement. The named plaintiff 

on the complaint is Kleen Products LLC. It asked the district 

court to certify the following class:

All persons that purchased Containerboard Products 

directly from any of the Defendants or their subsidiaries or affiliates for use or delivery in the United States 

from at least as early as February 15, 2004 through November 8, 2010.
Nos. 15-2385 & 15-2386 3

The proposed definition carved out the defendants themselves, entities or personnel related to them, and governmental entities. The Defendants opposed class certification on a 

number of grounds: whether common questions predominate; whether antitrust injury can be proved using a common 

method; whether the amount of damages can be proved using 

a common method; and whether a class action is superior. 

As the Supreme Court emphasized in Wal-Mart Stores, Inc. 

v. Dukes, 564 U.S. 338 (2011), “Rule 23 does not set forth a mere 

pleading standard. A party seeking class certification must affirmatively demonstrate his compliance with the Rule ... .” Id.

at 350. We must therefore take a careful look at the evidence 

that the Purchasers presented in support of class certification 

as we assess the district court’s ruling. Some of that evidence 

was provided by experts, but at this stage we need say little 

about them, because no defendant challenged the Purchasers’ 

experts under Federal Rule of Evidence 702 or the Supreme 

Court’s decision in Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 

579 (1993). See Tyson Foods, Inc. v. Bouaphakeo, 136 S. Ct. 1036, 

1049 (2016) (where there is no Daubert challenge, district court 

may rely on expert evidence for class certification). The district court also pointed out that “[f]or the most part, the parties agree on the basic facts, and both parties’ experts rely 

upon the same data, so there are little if any factual disputes 

that the Court must resolve to decide class certification.” For 

that reason, the court concluded that there was no need for a 

comprehensive evidentiary hearing. This, in our view, was a 

case-management decision that we have no reason to secondguess, despite Defendants’ complaints. See American Honda 

Motor Co. v. Allen, 600 F.3d 813, 815 (7th Cir. 2010) (evidentiary 

hearing should be held “if necessary”); West v. Prudential Sec., 

Inc., 282 F.3d 935, 938 (7th Cir. 2002) (same).
4 Nos. 15-2385 & 15-2386

Two final points are worth making before we turn to the 

evidence. First, nothing in Wal-Mart changed the applicable 

standard of review, which is deferential (as the cases say, only 

for “abuse of discretion”). Messner v. Northshore Univ. 

HealthSystem, 669 F.3d 802, 811 (7th Cir. 2012). Second, it remains true that Rule 23 does not demand that every issue be 

common; classes are routinely certified under Rule 23(b)(3) 

where common questions exist and predominate, even 

though other individual issues will remain after the class 

phase. See, e.g., McMahon v. LVNV Funding, 807 F.3d 872, 875–

76 (7th Cir. 2015); Pella Corp. v. Saltzman, 606 F.3d 391, 393 (7th 

Cir. 2010).

II

Although the requirements for class certification under 

Rule 23 are familiar, we set out the critical sections of the rule 

here for ease of reference:

(a) Prerequisites. One or more members of a class 

may sue or be sued as representative parties on behalf 

of all members only if:

(1) the class is so numerous that joinder of all 

members is impracticable;

(2) there are questions of law or fact common to 

the class;

(3) the claims or defenses of the representative 

parties are typical of the claims or defenses of 

the class; and

(4) the representative parties will fairly and adequately protect the interests of the class.

* * *
Nos. 15-2385 & 15-2386 5

(b) Types of Class Actions. A class action may be 

maintained if Rule 23(a) is satisfied and if:

* * *

(3) the court finds that the questions of law or 

fact common to class members predominate 

over any questions affecting only individual 

members, and that a class action is superior to 

other available methods for fairly and efficiently 

adjudicating the controversy. The matters pertinent to these findings include:

(A) the class members’ interests in individually controlling the prosecution or 

defense of separate actions;

(B) the extent and nature of any litigation 

concerning the controversy already begun by or against class members;

(C) the desirability or undesirability of 

concentrating the litigation of the claims 

in the particular forum; and

(D) the likely difficulties in managing a 

class action.

Our focus is on the predominance requirement of subpart 

(b)(3), since, as the district court noted, “Defendants have conceded that typicality, commonality, and adequacy have been 

satisfied so long as [Purchasers] have adequately proven predominance,” and no one is arguing about numbers either.

A

We begin with some background facts about the containerboard industry. “Containerboard” is the term for a sheet of 
6 Nos. 15-2385 & 15-2386

heavy paper with a smooth top and bottom (the linerboard) 

and a fluted layer between the two (the corrugated medium). 

It is made in large, expensive mills; as of 2008, no new mills 

had been built in the United States for more than 12 years. The 

containerboard sheets are cut and folded into products such 

as boxes of varying sizes. The industry is dominated by vertically integrated producers, which means simply that the fabrication of the containerboard and then its processing into final products are handled internally by a firm. This means, importantly for antitrust purposes, that the Purchasers bought 

directly from the alleged conspirators, not through intermediaries. See Illinois Brick Co. v. Illinois, 431 U.S. 720 (1977) (distinguishing between direct-purchaser suits, which are permitted under Clayton Act § 4, and indirect-purchaser suits, which 

are not). 

Containerboard is a commodity, sold in standardized 

compositions and weights. The final products are also standardized; one trade association commented that “boxes are essentially commodity items used in well established markets.” 

The most common containerboard product sold in the United 

States in 2010 was unbleached kraft linerboard weighing 42 

pounds per thousand square feet. Pulp & Paper Week (PPW), 

an industry periodical, publishes weekly price indices that include the price for the 42-pound linerboard for delivery east 

of the Rocky Mountains. The PPW index, as it is called, is 

widely used within the industry as a benchmark. 

A small and shrinking number of firms produce most of 

the containerboard in North America. As of 1997, the five 

largest firms (i.e. the current defendants or their predecessors) 

were responsible for 41% of North American production. By 

2007, the Defendants furnished 74% of that production. Add 
Nos. 15-2385 & 15-2386 7

in the next two firms, and the number swelled to 84%. (This 

evidence is ambiguous: a cartel’s market share will shrink

over time, to the extent that the high prices attract new entry 

from fringe competitors or imports, but its market share will 

grow to the extent that the cartel successfully uses exclusionary devices. The existing record does not resolve that ambiguity, but it does not matter for purposes of class certification.)

There was a great deal of evidence designed to show that 

the hypothesis that Defendants had organized a cartel was 

one that a jury could accept. We do not need to review all of 

it, but we offer some key points. During the class period, 

which ran from February 15, 2004, through November 8, 2010, 

Defendants attempted 15 price increases, and with one exception, all Defendants joined each one, at roughly the same time 

(11 out of 15 times within the same month). Twelve times out 

of 15 they increased prices by identical amounts; the remaining times the increases of different firms varied by less than 

2% of the average price. 

Capacity in the industry over this period was declining in 

North America, though increasing elsewhere; meanwhile, demand was constant or increasing. Defendants increased 

prices at least once during the recession of 2008 and 2009, and 

they raised prices again twice in 2010. Inventory levels were 

decreasing, because of several steps they took: they closed 

many mills; they indefinitely idled some; they temporarily 

idled others; and they slowed down production. In 2005, they 

announced mill closures representing 931,000 tons of capacity, and shortly thereafter they raised prices $30/ton. They did 

much the same thing in 2009. Communication among the Defendants was easy, thanks to trade associations. 
8 Nos. 15-2385 & 15-2386

These and other facts spurred the Purchasers to bring this 

suit and to structure it as a class action. They filed their motion for class certification only after extensive discovery. In 

that motion, they relied on the type of industry facts we have 

just mentioned, as well as on reports from two experts, Michael J. Harris and Mark Joseph Dwyer. Defendants countered with reports from two other experts, Dennis Carlton and 

Janusz Ordover. Harris concluded that the structure of the 

containerboard industry made it likely that a conspiracy 

among the Defendants could succeed in increasing prices for 

all or nearly all purchasers; he also opined that Defendants’ 

strategy would not have made sense if it had been undertaken 

unilaterally by each company. Carlton and Ordover disagreed, contending that Defendants’ pricing behavior could be 

explained by oligopolistic interdependence (that is, by parallel but independent behavior undertaken by firms in a concentrated market). They suggested ways in which the supply 

restrictions might have been rational under the circumstances. Tellingly, however, they never said that there might 

have been a cartel with respect to some purchasers and not 

with respect to others.

On the subject of damages, Purchasers’ expert Dwyer examined price movements. For example, he compared the actual prices paid by a sample of class members before and after 

the Defendants’ price increases and found that in 92% of cases 

those prices increased. He also constructed a regression 

model to estimate the overcharges made possible by the conspiracy. That model indicated that the class paid overcharges 

of approximately 3.08%, or in dollar terms, approximately 

$3.8 billion too much. Defendants’ experts criticized the sam-
Nos. 15-2385 & 15-2386 9

ple size that Harris had used, and they asserted that Purchasers’ experts had failed adequately to account for external factors influencing price and capacity.

B

The district court began its analysis of predominance—the 

central disputed issue in the case—by recalling the Supreme 

Court’s statement in Amchem Products, Inc. v. Windsor, 521 U.S. 

591 (1997), that “[t]he Rule 23(b)(3) predominance inquiry 

tests whether proposed classes are sufficiently cohesive to 

warrant adjudication by representation.” Id. at 623. It also 

acknowledged that, as the Supreme Court puts it, “Rule 

23(b)(3)’s predominance criterion is even more demanding 

than Rule 23(a).” Comcast Corp. v. Behrend, 133 S. Ct. 1426, 1432 

(2013). Predominance is satisfied when “common questions 

represent a significant aspect of a case and ... can be resolved 

for all members of a class in a single adjudication.” Messner,

669 F.3d at 815 (internal quotation marks omitted); see also 

Wal-Mart, 564 U.S. at 350 (a common contention for Rule 

23(a)(2) purposes “must be of such a nature that it is capable 

of classwide resolution—which means that determination of 

its truth or falsity will resolve an issue that is central to the 

validity of each one of the claims in one stroke”). With those 

principles in mind, the court evaluated the two central elements of the Purchasers’ case: the alleged violation of the antitrust laws, and the causal link between that violation and 

their alleged injury. It set the question of damages to one side, 

noting that “it is well established that the presence of individualized questions regarding damages does not prevent certification under Rule 23(b)(3).” Messner, 669 F.3d at 815 (citing 

Wal-Mart, 564 U.S. at 362 (“individualized monetary claims 

belong in Rule 23(b)(3)”)). 
10 Nos. 15-2385 & 15-2386

With respect to proof of liability, the court had this to say: 

To prove each element of a conspiracy, virtually all 

class members would be relying on the same evidence 

that Plaintiffs have submitted in support of class certification—namely, the documents, emails, phone records, and other indirect evidence necessary to prove 

that Defendants conspired in violation of antitrust 

laws. ... [I]t is much more efficient to have a single trial 

on the alleged conspiracy rather than thousands of 

identical trials all alleging identical conspiracies based 

on identical evidence.

While acknowledging that Defendants hotly contested the 

conspiracy allegation, the court found that their arguments 

went to the merits, not to the suitability of the case for class 

treatment.

Turning to causation, to which it also referred as “antitrust 

impact,” the court rejected the Defendants’ effort to equate 

this case to Comcast, where the Supreme Court found a mismatch between the plaintiffs’ damages theory and the evidence they presented to show predominance. First, on the 

question of impact, defined as whether Purchasers were 

harmed, the court found that at the class-certification stage 

the plaintiffs needed to demonstrate that the element of impact is capable of class-wide proof at trial, through evidence 

common to all class members. Looking at all the evidence, the 

court found this element satisfied. For example, the Defendants’ price increases were not tailored to each individual purchaser; this was a commodity market with a structure conducive to collusion; communications took place at a high level; 

the common use of the PPW index affected all market partic-
Nos. 15-2385 & 15-2386 11

ipants; and the Defendants lacked any other reasonable explanation for the tight correlation between the index and their

announcements of price increases. 

With respect to damages, the court found that the Purchasers had the burden of producing a reliable method of measuring classwide damages based on common proof. It rejected 

the Defendants’ argument that the eventual need to examine 

each individual purchaser’s damages was enough to defeat a 

finding of predominance. Nothing in Comcast, the court said, 

requires a different outcome. As this court noted in In re IKO 

Roofing Shingle Products Liability Litigation, 757 F.3d 599 (7th 

Cir. 2014), the plaintiffs’ damages expert in Comcast had estimated harm based on the assumption that all four theories of 

liability that plaintiffs offered had been established. The class 

certified by the court, however, was limited to only one of 

those theories. This, we explained, is what the Supreme Court 

said, “made class treatment inappropriate: without a theory 

of loss that matched the theory of liability, the class could not 

get anywhere.” Id. at 602. With that point established, the 

court assessed Dwyer’s report, concluded that both the methodology and the data were reliable, and concluded that it 

could be used to demonstrate class-wide damages.

Finally, the court held that Purchasers had shown the superiority of proceeding under Rule 23(b)(3). The fact that 

some class members had signed releases as a part of a settlement of an earlier class action (dealing with an alleged linerboard conspiracy that took place between 1993 and 1995) did 

not require a contrary finding. As the court said, 

[t]he conduct at issue in the prior litigation was Defendants’ allegedly collusive behavior in the mid-nineties. The actions at issue here are coordinated market 
12 Nos. 15-2385 & 15-2386

manipulation and price-increase announcements that 

occurred nearly a decade later. ... Under Defendants’ 

argument, they are free to keep colluding in violation 

of antitrust laws so long as they conspire in the same 

way as they were alleged to have behaved in a prior 

settled case. The Court is unaware of any case supporting this argument; indeed, several cases are to the contrary.

The court also rejected similar arguments based on particular 

contractual provisions, and it decided that retaining defendant Rock-Tenn in the case would not violate its bankruptcy 

discharge. 

C

1

We follow the same general outline that the district court 

used, looking first at predominance and then at superiority. 

Within predominance, we consider two points: whether common methods of proof can be used to demonstrate the existence of the alleged collusion and its effect on prices in the containerboard market; and whether the existence and impact of 

any such collusion predominate over other factors that may 

affect an individual plaintiff’s damages. These inquiries apply 

to all defendants. Defendant RockTenn raises some additional 

arguments related to its bankruptcy; we address these at the 

close of the opinion.

In order to secure class certification, the Purchasers had to 

demonstrate (not merely allege) that there is proof common 

to all class members, and that this proof would show that they 

suffered “injuries that reflect the anticompetitive effect of either the violation or the anticompetitive acts made possible by 
Nos. 15-2385 & 15-2386 13

the violation.” James Cape & Sons Co. v. PCC Const. Co., 453 F.3d 

396, 399 (7th Cir. 2006); see Brunswick Corp. v. Pueblo Bowl-OMat, Inc., 429 U.S. 477 (1977). 

Purchasers tendered extensive evidence that, if believed, 

would be enough to prove the existence of the alleged conspiracy. Not surprisingly, it is largely circumstantial. But they 

offered voluminous written materials of various types, which 

in the aggregate pointed to the existence of both agreement 

and actions to violate the antitrust laws. Indeed, Defendants 

do not contest that the existence of the conspiracy could be 

(perhaps had to be) proven by evidence common to the class. 

The more difficult question (though not too difficult in the 

end) is whether the common evidence could show the fact of 

injury on a classwide basis. See Messner, 669 F.3d at 819 (“The 

ability to use such common evidence and common methodology to prove a class’s claims is sufficient to support a finding 

of predominance on the issue of antitrust impact for certification under Rule 23(b)(3).”). At base, Defendants argue that it 

is not enough for Purchasers to prove aggregate injury and 

one aggregate overcharge, without allocating how much of 

that overcharge was paid by each individual class member. 

They urge that Purchasers have the burden of showing that 

every class member must prove at least some impact from the 

alleged violation. For that proposition, they rely on In re Hydrogen Peroxide Antitrust Litigation, 552 F.3d 305, 311 (3d Cir. 

2008), and In re Rail Freight Fuel Surcharge Antitrust Litigation, 

725 F.3d 244, 252 (D.C. Cir. 2013). 

While we have no quarrel with the proposition that each 

and every class member would need to make such a showing 

in order ultimately to recover, we have not insisted on this 

level of proof at the class certification stage. To the contrary, 
14 Nos. 15-2385 & 15-2386

we said in Suchanek v. Sturm Foods, Inc., 764 F.3d 750 (7th Cir. 

2014), that “[i]f the [district] court thought that no class can be 

certified until proof exists that every member has been 

harmed, it was wrong.” Id. at 757; see also Parko v. Shell Oil 

Co., 739 F.3d 1083, 1084–85 (7th Cir. 2014); McReynolds v. Merrill Lynch, Pierce, Fenner & Smith, Inc., 672 F.3d 482, 491 (7th 

Cir. 2012). There is no evidence to make us think that the class 

defined by the district court either excludes too many purchasers or contains troublesome internal conflicts, either of 

which would indicate it should be rejected. We therefore 

move on to the adequacy of the Purchasers’ showing that the 

conspiracy had an effect on the prices they paid.

The parties have jousted over the need for some kind of 

“but-for” analysis, by which Defendants mean an expert construction of a hypothetical market free of any anticompetitive 

restraint, to which the actual market can be compared. See 

Blades v. Monsanto Co., 400 F.3d 562, 569 (8th Cir. 2005). That 

might be one way in which a plaintiff could satisfy its burden, 

but we think that the formulation is too narrow. What is essential is whether the class can point to common proof that 

will establish antitrust injury (in the form of cartel pricing 

here) on a classwide basis. Like the district court, we are satisfied that Purchasers have done so.

The Purchasers built up their case with several types of 

evidence. First, expert Harris’s report showed that the structure of the containerboard market was conducive to successful collusion. He pointed to the concentration of manufacturers; the vertical integration of the market; the capital-intensive 

manufacturing process (which affected the pace and likelihood of new entry); weak competition from imported con-
Nos. 15-2385 & 15-2386 15

tainerboard; no good substitutes for the product; a low elasticity of demand; and a standardized, commodity product. 

These are all well accepted characteristics of a market that is 

subject to cartelization. See, e.g., In re Text Messaging Antitrust 

Litig., 782 F.3d 867, 872 (7th Cir. 2015); Minn-Chem, Inc. v. 

Agrium, Inc., 683 F.3d 845, 859–60 (7th Cir. 2012) (en banc); In 

re High Fructose Corn Syrup Litig., 295 F.3d 651, 657 (7th Cir. 

2002); Jack Walters & Sons Corp. v. Morton Bldg., Inc., 737 F.2d 

698, 710–11 (7th Cir. 1984).

Defendants pooh-pooh these cases as examples of the discredited structure-conduct-performance (SCP) paradigm that 

ruled antitrust from the 1950s until the mid-1970s. See, e.g., 

United States v. Von’s Grocery Co., 384 U.S. 270 (1966) (striking 

down a merger between a firm with 4.7% of the market and a 

firm with 4.2%). We put to one side the fact that the SCP paradigm was used during that era primarily in merger cases and 

this is a cartel case alleging hard-core price-fixing—the kind 

of case in which lack of market power or reasonableness of 

price is no defense. The evidence here goes well beyond the 

structural. The flaw in the old SCP notion was the thought 

that it was enough to know the structure of a market in order 

to predict what kind of conduct would ensue, and how competitively that market would perform. No such chain of assumptions taints the Purchasers’ proof. They have shown actual price increases, a mechanism for those increases, the communication channels the conspirators used, and factors suggesting that cartel discipline can be maintained. We are not 

saying that any of these points have been proven, of course, 

but we are saying that this evidence is enough to support class 

treatment of the merits. 
16 Nos. 15-2385 & 15-2386

Defendants also object to the Purchasers’ definition of the 

market. The Purchasers, they say, have conflated the market 

for containerboard (the material) with the market for finished 

corrugated products. The district court responded that the 

uniform vertical integration found in this industry makes it 

appropriate to look to the finished products. That is correct: 

Purchasers (and we) have no reason to dig inside the defendant companies to evaluate their internal pricing of the raw 

materials they use in producing the boxes and other products 

they sell. 

Next, Defendants criticize Dwyer’s examination of the 15 

price increases they announced and his use of the PPW index 

in that connection. He analyzed “industry-wide reflections of 

price and actual prices paid by class members before and after” the price-increase announcements, and he found that 

nine of the 15 efforts succeeded (i.e. resulted in a durable price 

increase). He also performed a regression analysis comparing 

classwide aggregate prices to the PPW index and found that 

“more than 97% of variation in aggregate prices is explained 

by changes in the index.” He reviewed 738 contracts (those 

the Defendants had produced) and found that 96% of them 

“contained provisions that tied pricing to the PPW index.” 

The Defendants protest that the Purchasers have shown only 

correlation, not causation, but we think, taking into account 

the rest of the evidence, Purchasers have not fallen into that 

trap. 

Defendants also argue that Dwyer’s approach is the same 

kind of “trial-by-formula” that the Supreme Court rejected in 

Wal-Mart. But in that case the Court disapproved the plaintiff’s attempt to take a sample of the class members, who al-
Nos. 15-2385 & 15-2386 17

leged employment discrimination, to determine what percentage of that sample had actually experienced discrimination, and then to extrapolate that percentage for the whole 

class. The Purchasers here are doing nothing of the sort: they 

assert that every person or entity in North America paid the 

overcharges that resulted from Defendants’ collusive practices. Even for transactions where prices were negotiated individually or a longer term contract existed, the district court 

found, reasonably, that the “starting point for those negotiations would be higher if the market price for the product was 

artificially inflated.” 

We have already discussed the Purchasers’ common proof 

of damages, but we add a few more words here to respond to 

the Defendants’ Comcast arguments. Defendants understand 

Comcast to hold that “individualized damages do foreclose 

predominance if plaintiffs present no classwide method to adjudicate damages tethered to their theory of antitrust violations and if resolving those individualized damages issues 

would ‘overwhelm questions common to the class.’” Brief for 

Appellants at 36 (quoting 133 S. Ct. at 1433). We agree with 

Defendants that Comcast insists that the damages theory must 

correspond to the theory of liability, but that is all Comcast said 

that is pertinent to our case. We must see if there is a classwide 

method for proving damages, and if not, whether individual 

damage determinations will overwhelm the common questions on liability and impact.

Dwyer conducted a preliminary analysis to demonstrate 

the feasibility of estimating damages on a classwide basis. He 

created two categories of products, intermediate and final, 

and he used two benchmark periods (before and after the 

class period) to compare prices. He also accounted for many 
18 Nos. 15-2385 & 15-2386

other variables, such as downstream demand, production and 

delivery, inflation, and seasonal factors, in order to control for 

other influences on price and to isolate the impact of the conspiracy. Using a “dummy variable,” he calculated an average 

overcharge of 2.92% for the final products category and 3.81% 

for the intermediate products category. He then multiplied 

the average overcharges by the dollar amount of purchases by 

class members, subtracting purchases that had taken place 

under previously contracted prices. He found that the class 

members paid $801.27 million more for intermediate products and $2.991 billion more for final products than they 

would have absent the conspiracy. 

Defendants complain that it is wrong to calculate aggregate rather than individual damages for the class. The district 

court rejected that position as a matter of law, as do we. We 

held in Loeb Indus., Inc. v. Sumitomo Corp., 306 F.3d 469 (7th Cir. 

2002), that plaintiffs are permitted to use estimates and analysis to calculate a reasonable approximation of their damages. 

Id. at 493. And we already have confirmed that at the class 

certification stage, plaintiffs are not obliged to drill down and 

estimate each individual class member’s damages. The determination of the aggregate classwide damages is something 

that can be handled most efficiently as a class action, and the 

allocation of that total sum among the class members can be 

managed individually, should the case ever reach that point. 

If in the end the Defendants win on the merits, this entire matter will be over in “one fell swoop.” (See WILLIAM 

SHAKESPEARE, MACBETH, act 4, sc. 3, l. 220 (David Bevington 

ed., Pearson Longman 6th ed. 2009.) If Purchasers prevail on 

the common issues, both liability and aggregate damages will 

be resolved. The district court did not commit reversible error 

when it concluded that the class issues predominated.
Nos. 15-2385 & 15-2386 19

2

Everything we have said thus far also points to the superiority of the class device for this case. We need to address 

only two potential flies in the ointment that Defendants see: 

first, the significance (if any) of certain releases that some class 

members signed; and second, the relevance of contract defenses that might apply. 

Some class members settled claims in an earlier lawsuit 

against the same companies, dealing with the same industry. 

Defendants represent that there are 39 relevant settlement 

agreements implicating almost 10,000 of the individual claims 

at issue. The Purchasers respond that these numbers are 

wrong, because they involve double-counting and give an exaggerated impression of the real number of affected class 

members, since most people who signed releases did so with 

multiple defendants. More importantly, Purchasers also note 

that the Defendants’ numbers imply that most people who 

signed releases did so after the events giving rise to the present case, whereas in reality the releases are heavily distributed toward the beginning of the class period or earlier. Purchasers suggest the simple expedient of limiting the recovery 

period for any class member who signed a release to purchases made after that release was signed. That strikes us as 

an easy and effective way to handle this problem. Moreover, 

as the district court observed, the fact that some plaintiffs released the defendants from further liability for their actions in 

the mid-1990s is not a life-time inoculation against antitrust 

liability in the same industry. 

The other contract defenses to which Defendants point involve such provisions as mandatory arbitration and mediation clauses, forum-selection clauses, jury waivers, provisions 
20 Nos. 15-2385 & 15-2386

shortening the statute of limitations, and clauses eliminating 

remedies such as treble damages. Taking these limitations 

into account, they say, will destroy the cohesion of the class. 

The problem is that Defendants are relying on a case that involved a class-action waiver: Lozano v. AT&T Wireless Services, 

Inc., 504 F.3d 718, 728 (7th Cir. 2007), and there is no such 

waiver here. The Purchasers point out that Defendants have 

identified only 190 class members affected by this group of 

limitations, out of over 100,000 notices that were sent out pursuant to Rule 23(c)(2)(B). As the record stands, this smattering 

of individual contract defenses does not undermine the superiority of the (b)(3) class action.

III

We noted earlier that defendant RockTenn is in a different 

position from the other defendants, because it filed for bankruptcy and received a discharge on June 30, 2010, approximately four months before the end of the class period. The 

district court refused to dismiss RockTenn on that basis because it found evidence that RockTenn re-joined the conspiracy after the discharge. (For example, on the very evening of 

the day when the discharge order was entered, RockTenn’s 

president sent an email stating “I assume we are announcing 

tomorrow,” after three other defendants announced a simultaneous price increase.) The court also found that RockTenn 

might be jointly and severally liable for actions undertaken by 

its co-conspirators before the discharge, based on its post-discharge participation. See Havoco of Am., Ltd. v. Shell Oil Co., 

626 F.2d 549, 554 (7th Cir. 1980) (“[A] co-conspirator who joins 

a conspiracy with knowledge of what has gone on before and 
Nos. 15-2385 & 15-2386 21

with an intent to pursue the same objectives may, in the antitrust context, be charged with the preceding acts of its co-conspirators.”).

The district court’s reasoning was sound. RockTenn is free 

to argue at trial that it did not re-join the conspiracy. There is 

no conflict with bankruptcy law, however, if it did so, because 

in that case its liability would be predicated on post-discharge 

conduct. To the extent that these nuances need to be brought 

to the jury’s attention, we are confident that the district court 

can do so through proper instructions. 

IV

We conclude by noting again the basis of our ruling. First, 

with respect to the central issue of class certification under 

Federal Rule of Civil Procedure 23(a) and (b)(3), the only contested points relate to predominance and superiority. Defendants did not challenge Purchasers’ experts under Daubert and 

Federal Rule of Evidence 702, and so we accept their reports 

for what they are worth at this stage. We did not discuss the 

opposing views expressed by Defendants’ experts because 

they did not undermine the class certification decision. Defendants’ experts’ reports will be important, we assume, at the 

merits stage, but the fact that class certification decisions must 

be supported by evidence does not mean that certification is 

possible only for a party who can demonstrate that it will win 

on the merits. 

We AFFIRM the class-certification order of the district 

court.