Judges as Gatekeepers: The Admissibility of Scientific Evidence Based on Novel Theories

• Author: Mr. Justice Sidney N. Lederman
• Pages: 475-505

Judges

as

Gatekeepers:

The

Admissibility

of

Scientific

Evidence

Based

on

Novel Theories

Mr.

Justice

Sidney

N.

Lederman

A.

FORENSIC SCIENCE

AND THE

COURTS:

AN

UNEASY

ALLIANCE

The

testimony

of

experts

is

commonplace

in

Canadian courtrooms.

Although courts have long recognized that

an

expert's

opinions

are

nec-

essary

to

provide

scientific

technical information that

is

likely

to be

out-

side

the

experience

and

knowledge

of the

judge

or

jury,

a

certain

amount

of

judicial scepticism

has

always

surrounded

such

evidence.

Perhaps

the

most strident criticism

was

expressed

by

Chief Justice

Bramwell

who,

after

listening

for a

considerable time

to

expert witness-

es

whose opinions were diametrically opposed, tersely remarked that

all

witnesses

can be

classified

as

follows: "Liars, damned liars

and

experts."1

Although

the

traditional concern

was

that

the

expert testimony

might well

be

influenced

by the

fact

that

the

expert

was

being paid

by

*

Of the

Superior Court

of

Justice, Ontario. This paper

was

originally

published

in J.

Bloom

and H.

Dumont, eds.,

Science, Truth

and

Justice

(Montreal:

Les

Edi-

tions Themis

/

Canadian Institute

for the

Administration

of

Justice, 2001)

and

was

updated

in

October

2002.

The

assistance

of two of my law

clerks

at the

Superior

Court

of

Justice,

Emily

Marrocco

and

John Provart,

in the

research,

preparation,

and

updating

of

this paper

is

gratefully acknowledged.

1 See P.

Anisman

and

R.F. Reid, eds.,

Administrative

Law

Issues

and

Practice

(Scar-

borough,

ON:

Carswell, 1995)

at

196, note

14.

475

476 MR.

JUSTICE SIDNEY

N.

LEDERMAN

one

side and,

thus,

might give evidence

in

less

than

an

independent

fashion,

the new

battle ground relates

to the

danger

of

experts introduc-

ing

what

has

been called pseudo-science

or

junk science into

the

court-

room.

This latest concern

may

have originated

in the

context

of

contin-

gency

fee

toxic

tort litigation

in the

United States.

A

"toxic tort"

is a

cause

of

action that arises when

a

plaintiff

has

developed

a

disease fol-

lowing long-term exposure

to a

physical agent

—

either

a

chemical

or a

form

of

energy such

as

electro-magnetic fields.

Typically,

it is

alleged

that

the

defendant's economic activity resulted

in the

plaintiff's

expo-

sure

to the

agent, thereby causing

the

plaintiff

harm. Courts essentially

have

had to

determine whether

the

plaintiff's

exposure

and

subsequent

disease

are

causally related,

or

whether they

are

associated merely

by

chance.

For

example,

did the

asbestos inhaled

by the

plaintiff

cause

his

or

her

lung

cancer?

Or did the

plaintiffs'

exposure

to

radiation

from

high-tension power lines,

or to

cellular phones, cause their cancer?

Did

the

anti-nausea drug taken

by the

plaintiff

cause

the

birth

defects

that

occurred

thereafter?

Expert

testimony

is

tendered with respect

to

causal knowledge

and

furtherance

of

justice.

The

expert

may

employ

the

causal concepts

of

sci-

ence

when expressing purely

scientific

knowledge. Indeed,

it is the

lay-

man's

lack

of

such specialized knowledge that

has

been

the

fundamental

justification

for the

receipt

of

such expert testimony.

But

many

of

these

causation

theories

are or

were

new and

their reliability

has

been questioned.

Concern about

the

reliability

of

expert evidence

has

extended

far

beyond tort

law to all

cases

in

which

scientific

evidence

is

sought

to be

introduced.

Historically, courts have treated science

as an

objective

and

dispassionate source

of

knowledge,

and not as a

source

of

error. Based

on

this

deferential view, courts found

it

unnecessary

to ask the

scientif-

ic

expert, "How

do you

know?"

In

reality,

however, science

is no

more

objective

and

free

of

bias

than

are

other areas

of

human

endeavour.

The

courts' absolute

faith

in

scientists,

therefore,

was

misplaced.

In

Canada,

this

concern found expression

not so

much

in the

context

of

toxic tort litigation,

but

rather

in

criminal

law and the

proliferation

of

expert

testimony

in the

field

of

human behavioural sciences. Liberal

admissibility resulted

in the

introduction

of

questionable theories that

may

have

led in

some situations

to

wrongful

convictions. Thus, while

evidence

of

recovered memory

of

sexual abuse years

after

the

event

in

question found

a

theoretical basis

in

expert testimony, many experts

in

the

same

field

have condemned

it as

"false

memory syndrome."2