a human-in-the-loop procedure (Figure 2). The procedure initially considered all available 10,927,595 clinical narrative notes associated with the 314,292 patients and ignored notes that did not contain any smoking-related keywords (e.g., “smok,” “tobac,” and “cig”). Once we identified a smaller set of notes, we used a randomly selected sample to observe small text blobs located next to smoking-related keywords. This allowed for the quick identification of expressions associated with smoking status and the classification of the expressions into the smoking-status classes. The manual evaluation continued until we identified a subjectively defined significant portion of the smoking-related distinctive expressions.

HOMOGENEOUS SMOKING-
RELATED EXPRESSIONS

We converted all identified expressions and notes into alphabetical-only representations (i.e., removed all numbers, spaces, and characters outside the 26 English letters) to create homogeneous representations of the expressions and to allow one-to-one matching when searching for an expression in a note. In clinical documentation, notes typically are heterogeneous and may contain dozens of similar expressions that describe the same smoking status. For instance, “smoked 2 packs per week” (an indication for past smoker) may be similar to variations in other notes, such as “smoked 5 packs per week” (a different number of packs and a tab) or “smoked: 4-6 packs per week” (a range for the number of packs, a hyphen, and multiple spaces). As such, we converted all identified smoking-related expressions to homogeneous representations of the expressions. The three exemplary sentences are represented by one homogeneous expression: “smokedpacksperweek.” An example for a note converted to an alphabetical-only representation is shown in Figure 3.

Of the hundreds of smoking-related expressions that we identified, we selected a cutoff threshold to highlight the expressions that are useful to the identification of smoking status in a variety of cohorts. We sampled 10,000 notes to present the prevalence of the

W

Figure 4. Most prevalent smoking-related expressions. The y-axis represents the percentage of notes that contain the expression within a sample of 10,000 randomly selected notes.

PPD=packs per day. (A) Current smoker. (B) Past smoker. (C) Never smoked.

0.45%

0.40%

0.35%

0.30%

0.25%

0.20%

0.15%

0.10%

0.05%

0.00%

c
ur
ren
ts
m
oker
co
nti
nu
e
st
os
m
oke
s
m
oki
ngp
pd
sm
oke
sp
pd
s
mo
kerp
pd
h
e
sm
o
ke
s
sti
ll
sm
o
ke
s
s
h
e
sm
o
ke
s
acti
v
es
m
oker
pp
ds
m
oker
c
urre
nt
ly
sm
o
ke
s
t
ob
acc
op
ackd
ay
d
o
e
ss
m
oke
p
ati
e
nt
sm
o
ke
s
(a)

1.10% 1.00%

0.90%

0.80%

0.70%

0.60%

0.50%

0.40% 0.30%

0.20%

0.10% 0.00%

q
uit
sm
oki
ng
pa
sts
m
oker
s
m
oked
ppd
s
m
oki
ngq
uit
t
ob
acc
oq
uit
h
es
m
oked
exs
m
oker
q
uit
to
bacco
u
s
edt
o
sm
oke
s
h
es
m
oked
s
m
okedp
ack
s
m
okedcig
are
tt
es
ha
s
n
ots
m
oked
si
nce
w
as
as
m
oker
s
m
oked
pac
ks
s
mo
kedi
nt
h
ep
ast
(b)

1.75%

1.50%

1.25%

1.00%

0.75%

0.50%

0.25%

0.00%

d
o
e
s
n
ots
m
oke
n
on
s
mo
ker
t
ob
acc
on
o
n
e
n
ev
era
s
mo
ker
s
m
oker
n
o
n
ev
ers
m
oke
sm
oke
n
o
n
os
m
oke
n
ota
s
mo
ker
d
o
e
s
nts
m
oke
(c)