FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

JUANITA STOCKWELL; MICHAEL

LEWIS; VINCE NEESON; GUILLERMO

L. AMIGO; E. R. BALINTON;

NIKOLAUS BORTHNE; EDWARD

BROWNE; PETER BUSALACCHI;

SILVIA DAVID; PHILIP FLECK;

SEVERO FLORES; GEORGE FOGARTY;

MALCOLM FONG; MARY GODFREY;

JASON HUI; JACKLYN M. JEHL;

RICHARD JUE; ROBERT LEUNG; PAUL

LOZADA; D.H. BUD MASSEY; BRUCE

MEADORS; THOMAS O’CONNOR;

SUSAN ROLOVICH; JESSIE

WASHINGTON; MICHAEL WELLS;

GARY CASTEL; BARTHOLOMEW

JOHNSON; MIKE BOLTE; JONES

JAMES,

Plaintiffs-Appellants,

v.

CITY AND COUNTY OF SAN

FRANCISCO,

Defendant-Appellee.

No. 12-15070

D.C. No.

4:08-cv-05180-

PJH

OPINION

Appeal from the United States District Court

for the Northern District of California

Phyllis J. Hamilton, District Judge, Presiding
2 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

Argued and Submitted

September 10, 2013—San Francisco, California

Filed April 24, 2014

Before: J. Clifford Wallace, Raymond C. Fisher,

and Marsha S. Berzon, Circuit Judges.

Opinion by Judge Berzon

SUMMARY*

Fed. R. Civ. P. 23(f) Class Certification

The panel in an interlocutory appeal reversed the district

court’s denial for want of commonality of a request under

Fed. R. Civ. P. 23(f) for certification of a class composed of

certain San Francisco Police Department officers.

The panel held that the district court abused its discretion

in denying class certification because of its legal error of

evaluating merits questions, rather than focusing on whether

the questions presented, whether meritorious or not, were

common to the members of the putative class. The panel held

that given the interlocutory nature of the appeal, and its

consequent limitation to class certification factors only, the

panel could not consider the merits questions, even as an

alternative ground for affirmance. The panel remanded to the

district court to consider in the first instance whether the

* This summary constitutes no part of the opinion of the court. It has

been prepared by court staff for the convenience of the reader.
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 3

putative class satisfied the strictures of Rule 23(b)(3), as well

as the other prerequisites for class certification.

COUNSEL

Michael S. Sorgen (argued), Andrea Adam Brott, and Ryan

L. Hicks, Law Offices of Michael S. Sorgen, San Francisco,

California; and Richard A. Hoyer, Hoyer and Associates, San

Francisco, California, for Plaintiffs-Appellants.

Christine Van Aken (argued), Deputy City Attorney, Dennis

J. Herrera, City Attorney, Elizabeth Salveson, Chief Labor

Attorney, and Jonathan C. Rolnick, Deputy City Attorney,

City of San Francisco, San Francisco, California, for

Defendant-Appellee.

OPINION

BERZON, Circuit Judge:

Several San Francisco police officers (“the plaintiffs” or

“the officers”) over the age of forty performed well enough

on an examination in 1998 to qualify for consideration for

promotion to Assistant Inspector. They allege that a new

policy of the San Francisco Police Department (“SFPD”)

abandoning the examination as a basis for certain assignments

worked a disparate impact based on age. The plaintiffs

sought certification of a class composed of all SFPD officers

over forty who had qualified on the 1998 examination.

The district court denied certification for want of

commonality. We permitted the officers to appeal the denial
4 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

of class certification under Federal Rule of Civil Procedure

23(f), and now reverse, holding improper the district court’s

reliance on merits issues unrelated to the pertinent

commonality inquiry.

I.

Nearly three and a half decades ago, the Civil Service

Commission of the City and County of San Francisco

(“City”) entered into a consent decree to settle allegations of

employment discrimination in the SFPD on the basis of race,

sex, and national origin, in violation of Title VII of the Civil

Rights Act of 1964, 42 U.S.C. § 2000e et seq.

In late 1998, the district court terminated that consent

decree. By stipulation of the parties, however, the district

court retained jurisdiction over issues related to a recently

administered promotional examination — the Q-35 Assistant

Inspector examination for promotion to the Investigations

Bureau — which the parties agreed would be governed by the

terms of the consent decree. On the same day, the district

court issued an order outlining promotion procedures for

officers who had sat for the Q-35 Assistant Inspector

examination. That order required a minimum of 175

Assistant Inspector appointments from the list of police

officers who had passed the examination, arranged in order of

exam performance (“Q-35 List”). The first 110 promotions

were to be made in rank order of performance. Subsequent

appointments, the court ordered, “will be made from a sliding

band that will start at rank 111. The band width is 84 points.” 

The district court authorized the City to review various

“secondary criteria” when making selections within that

sliding band. Between 1998 and 2006, the City selected 229
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 5

police officers from the Q-35 List for promotion to Assistant

Inspector.

In 2005, the Chief of Police announced a change in

promotion policy: To improve operational flexibility and

rationalize the promotional progression, the SFPD would no

longer promote Assistant Inspectors to the Investigations

Bureau from the Q-35 List. Instead, the SFPD would

administer a new Q-50 Sergeants examination and assign

some newly promoted Sergeants, selected on the basis of their

performance on the new exam, to the Investigations Bureau. 

Those Sergeants assigned to the Investigations Bureau would

have duties previously assigned to Assistant Inspectors.

The City administered the Q-50 Sergeants Examination

in 2006 and created a list of eligible officers (“Q-50 List”) the

following year. Soon thereafter, the SFPD began promoting

Sergeants from the recently compiled Q-50 List, many of

whom were given investigative duties. Assistant Chief

Morris Tabak agreed, in a deposition taken in this case, that

he knew of no reason “that those appointments could not have

been made from the Q-35 list[] that resulted from the 1998

exam.”

The officers initially filed this action in late 2008,

alleging that SFPD’s decision to use the Q-50 list instead of

the Q-35 list for investigative assignments both constituted a

pattern or practice of discrimination and generated a disparate

impact on older officers in violation of the Age

Discrimination in Employment Act (“ADEA”), 29 U.S.C.

§§ 621–634. They also alleged parallel violations of

California’s Fair Employment and Housing Act (“FEHA”),

Cal. Gov’t Code §§ 12940–12951.
6 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

The officers subsequently sought certification of a class

under their FEHA disparate impact claim. The district court

denied the motion for certification, explaining that the

officers failed to satisfy the requirements of both Federal

Rules of Civil Procedure 23(a)(2) and 23(b)(3).

After denial of certification, the officers filed a Second

Amended Complaint alleging only a disparate impact theory

of liability, again under both the ADEA and FEHA. Several

months later, the officers renewed their motion for class

certification of the FEHA claim,1

proposing as the class to be

certified SFPD “officers who were aged forty and older as of

each of the dates of the challenged appointments in 2007,

2008, and 2009 and who could have been appointed to

investigative positions had the City properly made

appointments from the Q-35 List.” The putative class defined

an officer “who could have been appointed,” as an officer

within the 84-point selection band at the time SFPD assigned

a sergeant to investigative work. The officers further

proposed the creation of separate subclasses for those who

could have been appointed at each date. Certification was

sought under Rule 23(b)(3). As the common question

required for certification, Fed. R. Civ. P. 23(a)(2), the officers

asserted a common question of fact: “[W]hether the City’s

employment practice of appointing Sergeants exclusively

from the Q-50 List to investigative positions traditionally

performed by Assistant Inspectors and refusing to make any

1 The officers also sought “conditional certification” of a collective

action under the ADEA on the ground that 29 U.S.C. § 216(b), which

governs collective actions under the ADEA, requires a lesser showing to

authorize aggregate litigation. For the purposes ofthis appeal, the officers

have forfeited that claim by failing to argue it in their briefs. See, e.g.,

Dream Games of Ariz., Inc. v. PC Onsite, 561 F.3d 983, 994–95 (9th Cir.

2009).
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 7

of the appointments from the active Q-35 List, had a disparate

impact on qualified applicants for the investigative positions

who were aged forty or above at the time of those

appointments, in violation of FEHA.”

The district court denied the renewed motion for class

certification for want of commonality. Having disposed of

the motion on that ground, the district court expressly

declined to rule on the officers’s argument that the putative

class satisfied the requirement of Rule 23(b)(3), which

requires both that common questions “predominate over any

questions affecting only individual members” of the class and

“that a class action is superior to other available methods for

fairly and efficiently adjudicating the controversy.”

The officers timely sought permission to appeal under

Rule 23(f), which authorizes discretionary review of an

interlocutory order granting or denying class certification. 

See Fed. R. Civ. P. 23(f); see also Chamberlan v. Ford Motor

Co., 402 F.3d 952, 959 (9th Cir. 2005) (per curiam)

(describing the standards we employ to guide our

discretionaryauthorization of appeals under Rule 23(f)). This

Court granted permission for the appeal, and the officers

timely perfected it. See Fed. R. App. P. 5(d).

II.

Federal Rule of Civil Procedure 23(a)(2) conditions class

certification on demonstrating that members of the proposed

class share common “questions of law or fact.” Such

commonality is one of four “threshold requirements”

contained in Rule 23(a); the other three are numerosity,
8 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

typicality, and adequacy of representation.2See, e.g.,

Amchem Prods., Inc. v. Windsor, 521 U.S. 591, 613 (1997). 

Together, these requirements seek to “limit the class claims

to those fairly encompassed by the named plaintiff’s claims.” 

Wal-Mart Stores, Inc. v. Dukes, 131 S. Ct. 2541, 2550 (2011)

(quoting Gen. Tel. Co. of Sw. v. Falcon, 457 U.S. 147, 156

(1982)) (internal quotation marks omitted).

Wal-Mart instructed that, although Rule 23(a)(2) refers to

common “questions of law or fact” in the plural, “‘[e]ven a

single [common] question’ will do.” Id. at 2556 (alterations

in original) (quoting id. at 2566 n.9 (Ginsburg, J.,

dissenting)). We have since clarified “that Rule 23(a)(2)

requires . . . ‘a single significant question of law or fact.’” 

Abdullah v. U.S. Sec. Assocs., Inc., 731 F.3d 952, 957 (9th

Cir. 2013) (emphasis in original) (quoting Mazza v. Am.

Honda Motor Co., 666 F.3d 581, 589 (9th Cir. 2012)).

 

2

 The text of the subsection is as follows:

(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.

Fed. R. Civ. P. 23(a).
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 9

Rule 23(a)(2) is not “a mere pleading standard,” so

establishing commonality sometimes requires affirmative

evidence, which the courts must subject to “rigorous

analysis.” Wal-Mart, 131 S. Ct. at 2551 (quoting Falcon,

457 U.S. at 161). Such rigor often “will entail some overlap

with the merits of the plaintiff’s underlying claim.” Id.

While some evaluation of the merits frequently “cannot be

helped” in evaluating commonality, id., that likelihood of

overlap with the merits is “no license to engage in freeranging merits inquiries at the certification stage.” Amgen

Inc. v. Conn. Ret. Plans & Trust Funds, 133 S. Ct. 1184,

1194–95 (2013). Instead, as the Supreme Court clarified last

year, “[m]erits questions may be considered to the extent —

but only to the extent — that they are relevant to determining

whether the Rule 23 prerequisites for class certification are

satisfied.” Id. at 1195 (emphasis added). “[W]hether class

members could actually prevail on the merits of their claims”

is not a proper inquiry in determining the preliminary

question “whether common questions exist.” Ellis v. Costco

Wholesale Corp., 657 F.3d 970, 983 n.8 (9th Cir. 2011).

Further, a common contention need not be one that “will

be answered, on the merits, in favor of the class.” Amgen,

133 S. Ct. at 1191. Instead, it only “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.” Wal-Mart, 131 S. Ct. at 2551 (emphases added). 

“To hold otherwise would turn class certification into a minitrial” on the merits, Ellis, 657 F.3d at 983 n.8, when the

purpose of class certification is merely“to select the metho[d]

best suited to adjudication of the controversy fairly and

efficiently,” Amgen, 133 S. Ct. at 1191 (alteration in original)

(internal quotation marks omitted).
10 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

Amgen, published over a year after the district court

decision here, illustrates well the application of the principle

that demonstrating commonality does not require proof that

the putative class will prevail on whatever common questions

it identifies. In Amgen, a class alleged securities fraud under

§ 10(b) of the Securities Exchange Act of 1934, 48 Stat. 891,

as amended, 15 U.S.C. § 78j(b), and Securities and Exchange

Commission Rule 10b–5, 17 C.F.R. § 240.10b–5. 133 S. Ct.

at 1191. To succeed on the merits, plaintiffs alleging

securities fraud under Rule 10b–5 “must prove ‘(1) a material

misrepresentation or omission by the defendant; (2) scienter;

(3) a connection between the misrepresentation or omission

and the purchase or sale of a security; (4) reliance upon the

misrepresentation or omission; (5) economic loss; and

(6) loss causation.’” Id. at 1192 (quoting Matrixx Initiatives,

Inc. v. Siracusano, 131 S. Ct. 1309, 1317 (2011)) (internal

quotation marks omitted). The fraud-on-the-market doctrine

“permits certain Rule 10b–5 plaintiffs to invoke a rebuttable

presumption of reliance on material misrepresentations aired

to the general public,” when those misrepresentations concern

securities traded in an efficient market. Id. To invoke the

fraud-on-the-market presumption, “plaintiffs must

demonstrate that the allegedmisrepresentations were publicly

known . . . , that the stock traded in an efficient market, . . .

that the relevant transaction took place ‘between the time the

misrepresentations were made and the time the truth was

revealed,’” Erica P. John Fund, Inc. v. Halliburton Co., 131

S. Ct. 2179, 2185 (2011) (quoting Basic Inc. v. Levinson,

485 U.S. 224, 248 n.27 (1988)), and that the

misrepresentations were material, Amgen, 133 S. Ct. at 1195.

Amgen held that where a class of investors seeks to rely

on the fraud-on-the-market presumption, proof of materiality

is unnecessary to certify a class under Rule 23(b)(3). Id. at
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 11

1191. The reasoning, in part, was that “[t]he alleged

misrepresentations and omissions, whether material or

immaterial, would be so equally for all investors composing

the class.” Id. at 1191. If the factfinder ultimately held those

representations immaterial, that determination would not

amount to “some fatal dissimilarity among class members

that would make use of the class-action device inefficient or

unfair. Instead, [it would generate] a fatal similarity —

failure of proof as to an element of the plaintiffs cause of

action.” Id. at 1197 (emphases added) (alteration omitted)

(quoting Richard A. Nagareda, Class Certification in the Age

of Aggregate Proof, 84 N.Y.U. L. Rev. 97, 107 (2009))

(internal quotation marks omitted). By its very nature, such

a similarity, whether fatal or not to the merits of the

materiality issue, is a common question. Although proof of

materiality was “an essential predicate of the fraud-on-themarket theory,” id. at 1195, the court held it “properly

addressed at trial or in a ruling on a summary-judgment

motion,” id. at 1197.

Notably, Amgen concerned satisfaction of Rule 23(b)(3),

which requires not merely a common question but also

“find[ing] that the questions of law or fact common to class

members predominate over any questions affecting only

individual members.” It held proof of a factor that would

ultimately be essential to success on the class’s claims not

merely unnecessary to demonstrate commonality, but also

unnecessary to demonstrate that such commonality

predominates. Rule 23(b)(3) imposes a “far more

demanding” standard than 23(a)(2). Amchem, 521 U.S. at

624. It was the less demanding standard of Rule 23(a)(2) that

was the basis of the district court’s denial of certification

here.
12 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

The principle that courts must consider merits issues only

as necessary to determine a pertinent Rule 23 factor, and not

otherwise, has special force at the appellate level where, as

here, we review a class certification determination under Rule

23(f). Under Rule 23(f), the limitation on consideration of

the merits to the relevant class certification questions is of

jurisdictional significance. Rule 23(f) permits discretionary,

interlocutory appeals “from an order granting or denying

class-action certification.” Fed. R. Civ. P. 23(f). 

Interlocutory appeals are, of course, “the exception rather

than the rule.” Chamberlan, 402 F.3d at 959. Absent Rule

23(f) or some other applicable exception, our jurisdiction

would be constrained by “‘the general rule that a party is

entitled to a single appeal, to be deferred until final judgment

has been entered.’” Mohawk Indus., Inc. v. Carpenter,

558 U.S. 100, 106 (2009) (quoting Digital Equip. Corp. v.

Desktop Direct, Inc., 511 U.S. 863, 868 (1994)); see also

28 U.S.C. § 1291. As the exception to the final judgment rule

created by Rule 23(f) applies only to class certification

decisions, merits inquiries unrelated to certification exceed

our limited Rule 23(f) jurisdiction, as well as the needs of

Rule 23(a)–(b). In contrast, were this an appeal from a final

judgment after a class was certified (or not certified) and the

merits then determined, we would have the option of

addressing the merits and, if we decided to hold against the

plaintiffs, not addressing the class certification question. We

must police the bounds of our jurisdiction vigorously here as

elsewhere, see, e.g., Crowley v. Bannister, 734 F.3d 967, 974

(9th Cir. 2013), and so may not ourselves venture into merits

issues unnecessary to the Rule 23 issue before us.
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 13

III.

With that background, we reach the only question

properly before us — whether the district court’s denial of the

officers’s motion for class certification was an abuse of

discretion. See Ellis, 657 F.3d at 980. An “error of law[,]

. . . . ‘reliance on an improper factor, . . . omission of a

substantial factor, or . . . a clear error of judgment in weighing

the correct mix of factors’” qualifies as an abuse of

discretion. Bateman v. Am. Multi-Cinema, Inc., 623 F.3d

708, 712 (9th Cir. 2010) (quoting In re Wells Fargo Mortg.

Overtime Pay Litig., 571 F.3d 953, 957 (9th Cir. 2009)). We

conclude that the district court erred in denying class

certification because of its legal error of evaluating merits

questions, rather than focusing on whether the questions

presented, whether meritorious or not, were common to the

members of the putative class. By doing so, the district court

made an error of law and relied on improper factors, thereby

abusing its discretion.

To assess whether the putative class members share a

common question, the answer to which “will resolve an issue

that is central to the validity of each one of the [class

members’s] claims,” we must identify the elements of the

class members’s case-in-chief. Wal-Mart, 131 S. Ct. at 2551. 

The requisite prima facie case for a disparate-impact age

discrimination claim under California’s FEHA is parallel to

that under the ADEA. See Katz v. Regents of the Univ. of

Cal., 229 F.3d 831, 835 (9th Cir. 2000); see also Clark v.

Claremont Univ. Ctr., 6 Cal. App. 4th 639, 666 (1992). 

Under both statutes, “a plaintiff must demonstrate ‘(1) the

occurrence of certain outwardly neutral employment

practices, and (2) a significantly adverse or disproportionate

impact on persons of a particular [age] produced by the
14 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

employer’s faciallyneutral acts or practices.’” Katz, 229 F.3d

at 835 (alteration in original) (quoting Palmer v. United

States, 794 F.2d 534, 538 (9th Cir. 1986)). This formulation

requires a plaintiff to “‘isolat[e] and identify[] the specific

employment practices that are allegedly responsible for any

observed statistical disparities.’” Smith v. City of Jackson,

544 U.S. 228, 241 (2005) (emphasis in original) (quoting

Wards Cove Packing Co. v. Atonio, 490 U.S. 642, 656

(1989)). The plaintiff must also demonstrate a causal

connection between those specific employment practices and

the asserted impact on those of a particular age. See, e.g.,

Lewis v. City of Chicago, 560 U.S. 205, 212 (2010); Katz,

229 F.3d at 836.3

Here, the officers have identified a single, wellenunciated, uniform policy that, allegedly, generated all the

disparate impact of which they complain: the SFPD’s

decision to make investigative assignments using the Q-50

List instead of the Q-35 List. Each member of the putative

3 The ADEA codifies “five affirmative defenses” at 29 U.S.C. § 623(f). 

Meacham v. Knolls Atomic Power Lab., 554 U.S. 84, 91 (2008) (quoting

Trans World Airlines, Inc. v. Thurston, 469 U.S. 111, 122 (1985))

(internal quotation marks omitted). An employer is not liable, for

example, for otherwise-prohibited actions “where age is a bona fide

occupational qualification reasonably necessary to the normal operation

of the particular business, or where the differentiation is based on

reasonable factors other than age . . . .” 29 U.S.C. § 623(f)(1); see also

29 U.S.C. § 623(f) (listing other defenses). The FEHA also contains

affirmative defenses for, inter alia, “bona fide occupational

qualification[s]” and employment actions based on business necessity. 

Cal. Gov’t Code § 12940; Cal. Code Regs. tit. 2, § 11010.

The availability of such defenses, however, is not pertinent to the

commonality question, as long as there is a common question as to the

officers’s prima facie case of disparate impact age discrimination.
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 15

class was on the Q-35 List. Each suffered the effects of its

elimination, whatever those were.

“Identifying a specific practice is not a trivial burden” in

age discrimination cases alleging disparate impact. 

Meacham, 554 U.S. at 101. Indeed, the first Supreme Court

case to recognize the viability of a disparate-impact theory

under the ADEA rejected the claim on the merits for “failure

to identify the specific practice being challenged,” among

other shortcomings. Smith, 544 U.S. at 241. Requiring

plaintiffs to name a specific employment practice “has bite,”

Meacham, 554 U.S. at 100, both on the merits and for

purposes of determining whether there is a common question

in a disparate impact case. Here, the putative class is

challenging a single employment practice: making

investigative assignments from the Q-50 List instead of the

Q-35 List.

Once a specific practice is identified in a disparate impact

case, the next — although not the only — question becomes

whether that practice had a disproportionate adverse impact

on otherwise eligible officers over forty. “Generally

disparate impact analysis is used in a class action, but it may

also form the basis of an individual claim.” Bacon v. Honda

of Am. Mfg., Inc., 370 F.3d 565, 576 (6th Cir. 2004); see also

Watson v. Fort Worth Bank & Trust, 487 U.S. 977, 983

(1988) (addressing an individual disparate impact claim);

Pottenger v. Potlatch Corp., 329 F.3d 740, 749–50 (9th Cir.

2003) (same). In whatever procedural guise a disparate

impact claim appears, the party asserting it must demonstrate

a statistical disparity affecting members of the protected
16 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

group. Absent such a group-based disparity, the claim fails,

whether it is articulated by an individual or a class.4

The officers produced a statistical study purportedly

showing a disparate impact. The district court, and the City,

critiqued that study as inadequate for — among other reasons

— failing to conduct a regression analysis to take account of

alternative explanations, unrelated to age, for any statistical

imbalance. But whatever the failings of the class’s statistical

analysis, they affect every class member’s claims uniformly,

just as the materiality issue in Amgen affected every class

member uniformly. Each member of the putative class

suffered the effects of eliminating the Q-35 List.5

If those

4 This feature of disparate impact analysis distinguishes it sharply from

the theory of disparate treatment. Disparate impact analysis addresses

itself “to the consequences of employment practices, not simply the

motivation.” Griggs v. Duke Power Co., 401 U.S. 424, 432 (1971). Such

discriminatory consequences are perceptible only in the aggregate, which

is why we require statistical evidence. By contrast, the crux of a disparate

treatment case is the subjective motivation for an adverse employment

decision. Although statistical evidence can support a disparate treatment

claim, as in the pattern-or-practice cases of the type addressed by WalMart, such evidence is only “probative of motive,” used for the purpose

of “creat[ing] an inference of discriminatory intent with respect to the

individual employment decision at issue.” Obrey v. Johnson, 400 F.3d

691, 694 (9th Cir. 2005) (emphasis added) (quoting Diaz v. Am. Tel. &

Tel., 752 F.3d 1356, 1363 (9th Cir. 1985)).

5 Contrary to the City’s argument, that is true with respect to those

members who took and succeeded on the new Q-50 examination, as they

lost the same promotional opportunityas their peers, regardless of whether

their subsequent actions entitled them to similar — but not identical —

promotional opportunities. Whether those individuals will be precluded

from obtaining any relief because of their promotions based on the Q-50

examination is a separate question, as is the impact of that question on the

Rule 23(b)(3) analysis to be conducted on remand, see infra Part IV.
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 17

effects amount to a disparate impact on account of age, it will

be so for all class members or for none; their claims rise and

fall together.

That the City primarily relies on Katz for its contrary

argument reveals the fallacy of its position. Katz considered

not class certification but an already certified class’s appeal

of an adverse judgment on the merits. 229 F.3d at 833.

In Katz, a class of laboratory employees claimed the

decision to offer certain early retirement incentives to

participants in the University of California Retirement Plan,

whose average age was 55, and not to participants in the

Public Employee Retirement System, whose average age was

60, generated a disparate impact on the basis of age. Id. at

833–34. We affirmed the district court’s judgment as a

matter of law against the plaintiffs, reasoning they had “failed

to demonstrate causation,” insofar as their statistical evidence

was “insufficient to raise an inference that the disparate

impact fell upon employees by virtue of their membership in

a protected age group.” Id. at 836. The failure to produce

statistics sufficient to demonstrate a causal relationship

between employee age and employer practice defeated the

claims of the entire class.

The same will be true here — the statistical showing of

disparate impact due to the challenged policy will either

succeed as to the class as a whole or, as the City argues, fail

— again, with respect to the class as a whole. In highlighting

the questions of statistical proof of disparate impact and

causation, the City has strengthened, not weakened, the case

for certification, as it has identified a common question, the

resolution of which will uniformly affect all members of the

class. And whether there is a disparate impact on the putative
18 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

class, to be established through statistical proof, is “a single

significant question of . . . fact,” Abdullah, 731 F.3d at 957

(emphasis in original) (internal quotation marks omitted), the

resolution of which is “central to the validity” of each of the

class members’s claims, Wal-Mart, 131 S. Ct. at 2551.

The City offers various reasons the putative class, or

various members of it, may not prevail, including: the

decision not to use the Q-35 List affected all officers on the

list equally, without regard to age; all the officers on the Q-35

List could have taken the Q-50 examination, so there was no

detrimental impact on them from the policy change; there

were no appointments of any Assistant Inspectors from 2007

through 2009, so the Q-35 List was inapplicable during that

period; and many of the class members would not have been

promoted even if the Q-35 List were used, as there would not

have been enough positions for all of them. Any and all of

these considerations may prove pertinent to the merits of the

case, and possibly to whether common issues predominate

under Rule 23(b)(3). But they do not eliminate the significant

common question we have identified, however that question

is ultimately answered and whether or not other, individual

questions are later determined to predominate.

In short, the officers are all challenging a single policy

they contend has adversely affected them. The question

whether the policy has an impermissible disparate impact on

the basis of age necessarily has a single answer. To so

recognize is in no way to approve of the statistical showing

the officers have made as adequate to make out their merits

case. Nor does identifying a common question sufficient for

Rule 23(a)(2) purposes entail any disagreement with the

City’s contention that proper statistical analysis would negate

any disparate impact traceable to age — or, for that matter, to
STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO 19

prejudge any other argument or defense the City may offer. 

The defects the City has identified may well exist, but they go

to the merits of this case, or to the predominance question,

see infra Part IV. Given the interlocutory nature of this

appeal, and its consequent limitation to class certification

factors only, we may not consider the merits questions, even

as an alternative ground for affirmance.

IV.

Having disposed of the officers’s certification motion for

want of commonality, the district court expressly declined to

evaluate the putative class’s argument that it satisfied the

predominance and superiority requirements of Rule 23(b)(3). 

The City now contends that “individual questions will

predominate with respect to [the officers’s] claims including:

(a) whether an officer took the 2006 Sergeants exam or not;

(b) comparisons of individual rank on and between the 1998

Assistant Inspector list and the 2007 Sergeant list; (c) the

relative qualifications of each officer on the list; and,

(d) other factors affecting an assignment to the Investigations

Bureau.” The City may or may not be correct. But those

questions, as they affect predominance, have been

inadequately briefed here. They have no effect on

commonality, because there is a single, logically prior,

common question: whether the cancellation of the Q-35 List

generated a disparate impact on older officers.

The effect of the questions the City raises on the

predominance inquiry are best addressed by the district court,

which is “‘in the best position to consider the most fair and

efficient procedure for conducting any given litigation,’

Doninger v. Pac. N.W. Bell, Inc., 564 F.2d 1304, 1309 (9th

Cir. 1977), and so must be given ‘wide discretion’ to evaluate
20 STOCKWELL V. CITY & CNTY. OF SAN FRANCISCO

superiority [under Rule 23(b)(3)], Lerwill v. Inflight Motion

Pictures, Inc., 582 F.2d 507, 512 (9th Cir. 1978).” Bateman,

623 F.3d at 712 (citation formatting in original). We thus

REMAND to the district court to consider in the first instance

whether the putative class satisfies the strictures of Rule

23(b)(3), as well as the other prerequisites for class

certification.

V.

We REVERSE the district court’s denial of certification

for want of commonality. That determination was an abuse

of discretion, as it disregarded the existence of common

questions of law and fact and impermissibly addressed the

merits of the class’s claims.

REVERSED and REMANDED.