81
ORIGINAL SCIENTIFIC ARTICLE
Reliability and validity of the Slovenian Translation of the Functional Oral Intake Scale (FOIS-SI)
Copyright (c) 2022 Slovenian Medical Journal. This work is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Reliability and validity of the Slovenian Translation of 
the Functional Oral Intake Scale (FOIS-SI)
Zanesljivost in veljavnost lestvice funkcionalnega peroralnega vnosa (angl. Functional 
Oral Intake Scale, FOIS-SI) v slovenskem prevodu
Barbara Vogrinčič,1 Klara Trpkova,1 Fajko Bajrović1,2
Abstract
Background: It is crucial that each and every stroke patient gets a systematic assessment of swallowing disorders, per-
formed by a dysphagia specialist. Therefore, there is a need to use a standardized scale among professionals. The aim of 
this study was to translate, adapt, and obtain the statistical characteristics of the Functional Oral Intake Scale (FOIS), which 
is an observer-rated dysphagia severity scale primarily developed for stroke patients, into the Slovenian language.
Methods: We performed a 5-step translation and adaptation process. Six speech and language pathologists had evaluated 
30 clinical records of patients with an acute ischemic stroke in the carotid artery territory with the Slovenian translation 
of the Functional Oral Intake Scale (FOIS-SI). Every clinical record included a speech and language clinical bedside assess-
ment of dysphagia, the sex, age, National Institutes of Health Stroke Scale (NIHSS), comorbidities of patients and lesion 
location. We examined interrater and intrarater reliability and additionally convergent validity of FOIS-SI with the theoret-
ically related IDDSI-Functional Diet Scale (IDDSI-FDS).
Results: The average measure Intraclass Correlation Coefficient (ICC) for the interrater reliability (ICC=0.959) and the intr-
arater reliability (ICC=0.979 and ICC=0.991) for both raters was excellent. The FOIS-SI scores correlated very high with the 
IDDSI-FDS (rs=0.927).
Conclusion: The results of this study show that the Slovenian translation of the FOIS has an excellent interrater and intra-
rater reliability and very high validity, which implies the FOIS-SI can be used as a tool to quantitatively assess the severity 
of dysphagia in clinical practice and research in patients with stroke in carotid artery territory across the country in all 
medical and care settings.
Slovenian Medical Journallovenian Medical Journal
1 Division of Neurology, University Medical Centre Ljubljana, Ljubljana, Slovenia
2 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
Correspondence / Korespondenca: Barbara Vogrinčič, e: barbara.vogrincic@kclj.si
Key words: dysphagia; rehabilitation; IDDSI; speech and language pathologist; ischaemic stroke
Ključne besede: disfagija; rehabilitacija; IDDSI; logoped; ishemična kap
Received / Prispelo: 6. 10. 2020 | Accepted / Sprejeto: 26. 11. 2020
Cite as / Citirajte kot: Vogrinčič B, Trpkova K, Bajrović F. Reliability and validity of the Slovenian Translation of the Functional Oral Intake 
Scale (FOIS-SI). Zdrav Vestn. 2022;91(3–4):81–90. DOI: https://doi.org/10.6016/ZdravVestn.3167
eng slo element
en article-lang
10.6016/ZdravVestn.3167 doi
6.10.2020 date-received
26.11.2020 date-accepted
Neurology, neuropsychology, neurophysiology Nevrologija, nevropsihologija, nevrofiziologija discipline
Original scientific article Izvirni znanstveni članek article-type
Reliability and validity of the Slovenian 
Translation of the Functional Oral Intake Scale 
(FOIS-SI)
Zanesljivost in veljavnost lestvice funkcionalnega 
peroralnega vnosa (angl. Functional Oral Intake 
Scale, FOIS-SI) v slovenskem prevodu
article-title
Reliability and validity of the Slovenian 
Translation of the Functional Oral Intake Scale 
(FOIS-SI)
Zanesljivost in veljavnost lestvice funkcionalnega 
peroralnega vnosa (angl. Functional Oral Intake 
Scale, FOIS-SI) v slovenskem prevodu
alt-title
dysphagia, rehabilitation, IDDSI, speech and 
language pathologist, ischaemic stroke
disfagija, rehabilitacija, IDDSI, logoped, ishemična 
kap kwd-group
The authors declare that there are no conflicts 
of interest present.
Avtorji so izjavili, da ne obstajajo nobeni 
konkurenčni interesi. conflict
year volume first month last month first page last page
2022 91 3 4 81 90
name surname aff email
Barbara Vogrinčič 1 barbara.vogrincic@kclj.si
name surname aff
Fajko Bajrović 1,2
Klara Klara Trpkova 1
eng slo aff-id
Division of Neurology, University 
Medical Centre Ljubljana, 
Ljubljana, Slovenia
Nevrološka klinika, Univerzitetni 
klinični center Ljubljana, 
Ljubljana, Slovenija
1
Faculty of Medicine, University 
of Ljubljana, Ljubljana, Slovenia
Medicinska fakulteta, Univerza v 
Ljubljani, Ljubljana, Slovenija 2
82
NEUROLOGY, NEUROPSYCHOLOGY, NEUROPHYSIOLOGY
Zdrav Vestn | March – April 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3167
1 Introduction
Swallowing is a complex physiological process, in 
which the activity of 50 pairs of muscles is orchestrated 
by an extensive neuronal network in the central nervous 
system to intake food into the mouth, prepare it and 
transport it from the oral cavity through the pharynx 
to the stomach (1,2). This process can be disturbed in 
many ways, which can lead to malnutrition, dehydra-
tion, and possibly death (3). Therefore, dysphagia is a 
common problem in all stages of swallowing. Accord-
ing to our clinical experience at the University Medical 
Centre (UMC) Ljubljana in the last years, dysphagia ap-
pears in 20% of stroke patients admitted for treatment 
to the Division of Neurology (unpublished clinical da-
ta). Globally the percentage is higher, around 50% (4). 
In the diagnostic process of dysphagia, a full bedside 
clinical examination is of utmost importance before ob-
jective methods, such as Videofluoroscopic Swallowing 
Study (VFSS) and Fiberoptic Endoscopic Evaluation of 
Swallowing (FEES), are eventually applied (5). Clinical 
swallowing bedside examination, VFSS, and FEES are 
mostly qualitative studies, which have limited options 
to precisely determine the severity of dysphagia. Yet, 
different follow-up methods for assessing dysphagia are 
also known to not be fully accurate. As a result, research-
ers developed quantitative scales based on both, VFSS 
and FEES techniques (6,7). However, not all patients 
have access to objective techniques, especially patients 
in general practices or nursing care facilities (8). There-
fore, different self-evaluating questionnaires and scales 
which could help clinicians to determine the severity of 
Izvleček
Izhodišča: Pri bolnikih z disfagijo po ishemični možganski kapi v povirju karotidne arterije, ki jih obravnava specialist za 
disfagijo, je ključno sistematično vrednotenje stopnje disfagije. Zato strokovnjaki izražajo potrebo po uporabi standardi-
zirane lestvice. Cilj raziskave je prevod in prilagoditev lestvice funkcionalnega peroralnega vnosa (angl. Functional Oral 
Intake Scale, FOIS), primarno sestavljene za bolnike po možganski kapi, ki je zdravnikom v pomoč pri vrednotenju izraže-
nosti disfagije. Preverili smo tudi zanesljivost in veljavnost lestvice funkcionalnega peroralnega vnosa (FOIS-SI).
Metode: Izveden je bil 5-stopenjski proces prevoda in prilagoditve. Šest izkušenih logopedov, ki se ukvarjajo z disfagijo, je 
ovrednotilo 30 kliničnih poročil bolnikov po ishemični možganski kapi v povirju karotidne arterije. Poročila so vsebovala 
klinično logopedsko obposteljno oceno disfagije, spol in starost bolnika, ter lestvico Nacionalnega inštituta za zdravje za 
oceno nevrološke prizadetosti po možganski kapi (NIHSS), pridružene bolezni in mesto spremembe. Na podlagi podatkov 
smo izračunali zanesljivost. Študija veljavnosti je bila izvedena z iskanjem povezave med FOIS-SI in lestvico izraženosti 
disfagije IDDSI-FDS.
Rezultati: Zanesljivost med logopedi je bila odlična (ICC=0.959). Prav tako je bila odlična zanesljivost ob ponovnem vred-
notenju (ICC=0.979 in ICC=0.991). V študiji smo zaznali zelo visoko korelacijo z IDDSI-FDS (rs=0.927).
Zaključek: Rezultati študije so pokazali, da je slovenska različica FOIS izjemno zanesljiva ter zelo visoko veljavna, kar naka-
zuje, da se FOIS-SI kot kvalitativno orodje za oceno izraženosti disfagije lahko uporablja v klinične in raziskovalne namene.
dysphagia were developed. In Table 1 the characteristics 
of published and available swallowing scales are listed. 
Regarding dysphagia, only the questionnaire Quality of 
life in swallowing disorders (9) is translated and adapted 
to the Slovenian language. To compare the patient’s level 
of dysphagia and outcome, a Slovenian translation of the 
severity scale is still needed. Since the Functional Oral 
Intake Scale (FOIS) has good psychometric character-
istics (10), correlates significantly with the Food Intake 
Level scale, swallowing time of the Functional Assess-
ment Measure, Mass Assessment of Swallowing Ability, 
Modified Barthel Index score, modified Rankin scale, 
VFSS (11), is easy to use, was translated to and validat-
ed in different languages (12-14), and was also used for 
different populations (11), and diseases (15-23), we de-
cided to translate it and evaluate the initial psychometric 
characteristics of the Slovenian translation.
FOIS was developed based on reviewing dyspha-
gia-related literature. The most describable items of a pa-
tient’s oral or compensatory intake of food and liquids, 
and its potential modification, were selected for the final 
scale form. The initial scale had 10 levels, but this num-
ber was reduced to seven after the pilot study (10).
2 Methods
This paper is part of a larger research about dysphagia 
outcome of stroke survivors in acute care, which was ap-
proved by the National Medical Ethics Committee of the 
Republic of Slovenia (No. 0120-255/2029/3, 14.07.2020). 
83
ORIGINAL SCIENTIFIC ARTICLE
Reliability and validity of the Slovenian Translation of the Functional Oral Intake Scale (FOIS-SI)
Sc
al
e 
(r
ef
er
en
ce
)
Fu
ll 
na
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re
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 se
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je
ct
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e 
as
se
ss
m
en
t
Po
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n
Re
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an
d 
va
lid
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co
m
m
en
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sp
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m
e 
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d 
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ve
rit
y 
Sc
al
e
7
Fr
om
 1
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ev
er
e 
dy
sp
ha
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PO
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ll 
pe
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ut
rit
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w
ith
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or
m
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VF
SS
Ad
ul
ts
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pr
es
en
tin
g 
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ffe
re
nt
 
di
ag
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ne
ur
ol
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ge
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ul
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ca
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Dy
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se
ve
rit
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ra
tin
g 
sc
al
e
0-
12
Fr
om
 0
 (b
es
t)
 to
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2 
(w
or
st
)
no
Ad
ul
ts
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ith
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os
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xc
el
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om
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o 
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ep
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ar
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d 
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tie
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hr
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ea
ls
 
or
al
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re
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rim
ar
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sc
ul
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sp
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ro
m
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ro
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m
ic
 d
ys
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n 
ca
nc
er
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nd
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er
vi
ca
l s
pi
ne
 
in
ju
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te
rr
at
er
 re
lia
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lit
y 
ra
ng
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fro
m
 0
.7
0 
to
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0
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te
rr
at
er
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lia
bi
lit
y 
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ng
ed
 
fro
m
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3 
to
 0
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0.
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nv
er
ge
nt
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al
id
ity
 - 
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gh
ly
 
as
so
ci
at
ed
 w
ith
 F
O
IS
 (p
=0
.9
6 
-0
.9
9)
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gr
ee
 o
f p
at
ie
nt
’s 
in
ta
ke
 o
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oo
d 
no
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or
al
ly
 o
r o
ra
lly
. 
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SS
 (2
7)
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nc
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na
l 
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ut
co
m
e 
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al
lo
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in
g 
Sc
al
e
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om
 0
 (n
or
m
al
 
fu
nc
tio
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an
d 
as
ym
pt
om
at
ic
) t
o 
V 
(n
on
or
al
 fe
ed
in
g 
fo
r 
al
l n
ut
rit
io
n)
ye
s
Fu
ll 
sp
ec
tr
um
 o
f 
or
op
ha
ry
ng
ea
l d
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ph
ag
ia
 
in
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lly
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ng
 
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s a
nd
 p
at
ie
nt
s w
ith
 
he
ad
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k 
ca
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, 
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ur
ol
og
ic
 d
is
or
de
rs
, 
ga
st
ro
es
op
ha
ge
al
 
co
nd
iti
on
s,
 a
nd
 p
sy
ch
ia
tr
ic
 
pr
ob
le
m
s.
N
o 
fo
rm
al
 st
ud
y.
Ph
ys
io
lo
gi
ca
l 
fu
nc
tio
n,
 w
ay
 o
f 
fe
ed
in
g,
 n
ut
rit
io
na
l 
an
d 
re
sp
ira
to
ry
 
st
at
us
. 
Ta
bl
e 
1:
 C
ha
ra
ct
er
is
tic
s 
of
 d
iff
er
en
t s
ca
le
s 
of
 th
e 
se
ve
rit
y 
of
 d
ys
ph
ag
ia
. T
he
 fu
ll 
na
m
e,
 le
ve
ls
, a
nd
 d
ire
ct
io
ns
 o
f t
he
 s
ev
er
ity
 o
f e
ac
h 
sc
al
e 
ar
e 
sh
ow
n.
 A
dd
iti
on
al
ly
, 
th
er
e 
is
 a
n 
ex
pl
an
at
io
n 
de
ta
ili
ng
 w
he
th
er
 o
r n
ot
 th
e 
sc
al
e 
re
qu
ire
s a
n 
ob
je
ct
iv
e 
as
se
ss
m
en
t, 
su
ch
 a
s t
he
 V
id
eo
flu
or
os
co
pi
c S
w
al
lo
w
in
g 
St
ud
y 
(V
FS
S)
 o
r t
he
 F
ib
er
op
tic
 
En
do
sc
op
ic
 E
va
lu
at
io
n 
of
 S
w
al
lo
w
in
g 
(F
EE
S)
 a
nd
 fo
r w
hi
ch
 p
op
ul
at
io
n 
th
e 
sp
ec
ifi
c s
ca
le
 is
 m
os
t s
ui
ta
bl
e.
 F
ur
th
er
m
or
e,
 th
e 
m
os
t r
ec
en
t p
sy
ch
om
et
ric
 ch
ar
ac
te
ris
tic
s 
an
d 
re
co
m
m
en
da
tio
ns
 o
f e
ac
h 
sc
al
e 
ar
e 
al
so
 m
en
tio
ne
d.
84
NEUROLOGY, NEUROPSYCHOLOGY, NEUROPHYSIOLOGY
Zdrav Vestn | March – April 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3167
Sc
al
e 
(r
ef
er
en
ce
)
Fu
ll 
na
m
e
Le
ve
ls
Di
re
ct
io
n 
of
 se
ve
ri
ty
Re
qu
ir
es
 a
n 
ob
je
ct
iv
e 
as
se
ss
m
en
t
Po
pu
la
tio
n
Re
lia
bi
lit
y 
an
d 
va
lid
ity
Re
co
m
m
en
da
tio
ns
FO
IS
 (1
0)
Fu
nc
tio
na
l O
ra
l 
In
ta
ke
 S
ca
le
7
Fr
om
 0
 (n
ot
hi
ng
 b
y 
m
ou
th
) t
o 
7 
(to
ta
l 
or
al
 in
ta
ke
 w
ith
 n
o 
re
st
ric
tio
ns
)
no
In
iti
al
ly
 fo
r s
tr
ok
e 
pa
tie
nt
s,
 
aft
er
w
ar
d 
st
ud
ie
s i
n 
tr
au
m
at
ic
 b
ra
in
 in
ju
ry
 (T
BI
), 
he
ad
 a
nd
 n
ec
k 
ca
nc
er
, 
vo
ca
l f
ol
d 
im
m
ob
ili
ty
, 
va
ga
l s
ch
w
an
no
m
a 
re
se
ct
io
n,
 c
er
eb
ra
l p
al
sy
, 
po
st
su
rg
ic
al
 d
ys
ph
ag
ia
, 
ne
ur
od
eg
en
er
at
iv
e 
di
se
as
es
, 
po
st
-e
xt
ub
at
io
n 
dy
sp
ha
gi
a 
in
 c
hi
ld
re
n,
 n
eu
ro
ge
ni
c 
dy
sp
ha
gi
a.
St
ro
ke
 –
 h
ig
h 
in
te
rr
at
er
 
re
lia
bi
lit
y 
(8
5%
), 
hi
gh
 c
rit
er
io
n,
 
an
d 
co
ns
en
su
al
 v
al
id
ity
.
Fo
od
 re
st
ric
tio
n 
an
d 
w
ay
 o
f f
ee
di
ng
.
FO
IS
 fo
r 
in
fa
nt
s (
11
)
Fu
nc
tio
na
l O
ra
l 
In
ta
ke
 S
ca
le
5
Fr
om
 0
 (n
ot
hi
ng
 
by
 m
ou
th
) t
o 
5 
(e
xp
an
si
on
 o
f o
ra
l 
di
et
 re
ac
he
d)
no
Th
e 
ge
ne
ra
l p
op
ul
at
io
n 
of
 
in
fa
nt
s w
ith
 d
ys
ph
ag
ia
.
H
ig
h 
in
te
r-
ra
te
r r
el
ia
bi
lit
y 
(9
5.
5%
) a
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co
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e 
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 9
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, p
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EO
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(2
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at
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ith
 
0 
(p
ro
bl
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r 1
 
(w
ith
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t a
 p
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).
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rly
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tis
fy
in
g 
va
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 a
nd
 
re
lia
bi
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y.
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 id
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s.
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IS
A 
(3
0)
M
cG
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ax
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29
 
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(h
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 o
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s
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ar
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te
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at
er
 
ag
re
em
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t (
0.
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an
d 
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ill
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SS
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s w
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n,
 
w
ay
 o
f f
oo
d 
in
ta
ke
.
85
ORIGINAL SCIENTIFIC ARTICLE
Reliability and validity of the Slovenian Translation of the Functional Oral Intake Scale (FOIS-SI)
This particular study was divided into two phases. Phase 
one was dedicated to the translation process, and phase 
two was focused on the study of reliability and validity 
of the Slovenian translation of FOIS (FOIS-SI) among 
clinicians.
2.1 Instrument description
2.1.1 Functional Oral Intake Scale
FOIS is a reliable scale to assess the functional sever-
ity of dysphagia. Observer-rated ordinal severity scale 
consists of seven levels, from nonoral feeding (Level 
1) to oral feeding without any restrictions (Level 7). To 
quantify dysphagia severity, clinicians may obtain the 
level of dysphagia of a patient through medical charts, 
dietary diaries and/or verified patient reports (10).
2.1.2 Translation
Permission for translation was obtained from the au-
thor of the original FOIS scale (10). The translation was 
performed according to WHO guidelines of translation 
and adaptations of instruments (32). The phases were 
followed: (i) the initial translation from English to Slove-
nian was performed by two speech and language pathol-
ogists (SLPs); (ii) The synthesis of two translations was 
made to provide the initial version; (iii) Back-translation 
was performed by an independent translator, who did 
not know FOIS. Furthermore, discrepancies were dis-
cussed between SLPs and independent translators until 
the complete Slovenian version; (iv) The final Slovenian 
translation was obtained, and the complete version was 
pre-tested; (v) Finally, the complete version was final-
ized (see Table 2).
Table 2: Original Functional Oral Intake Scale (FOIS) and Slovenian translation of FOIS (FOIS-SI).
Functional Oral Intake Scale (FOIS)
Tube dependent (Levels 1-3)
1 No oral intake
2 Tube dependent with minimal/inconsistence oral intake
3 Tube dependent with consistent oral intake of food or liquid
Total oral intake (Levels 4-7)
4 Total oral intake of a single consistency
5 Total oral intake of multiple consistency requiring special preparation.
6 Total oral intake with no special preparation, but must avoid specific foods or liquid items
7 Total oral intake with no restrictions
Lestvica funkcionalnega peroralnega vnosa (FOIS-SI)
Odvisnost od hranilne cevke (raven 1-3)
1 Brez peroralnega vnosa.
2 Odvisnost od hranilne cevke z minimalnim/občasnim peroralnim vnosom.
3 Odvisnost od hranilne cevke z rednim peroralnim vnosom.
Popoln peroralni vnos (raven 4-7)
4 Popoln peroralni vnos z eno konsistenco.
5 Popoln peroralni vnos z več konsistencami, ki zahtevajo poseben način priprave.
6 Popoln peroralni vnos brez posebne priprave, a z izogibanjem določenih izdelkov hrane/pijače.
7 Popoln peroralni vnos brez omejitev.
86
NEUROLOGY, NEUROPSYCHOLOGY, NEUROPHYSIOLOGY
Zdrav Vestn | March – April 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3167
2.1.3 Subjects
The clinical records of 30 patients with an acute isch-
emic stroke in the carotid artery territory, who were 
hospitalized at the Division of Neurology of the UMC 
Ljubljana, Slovenia, were reviewed and sent to six SLPs. 
Included with the clinical records was a report of speech 
and language clinical bedside assessments of dysphagia 
(CBAD), sex, age, National Institutes of Health Stroke 
Scale (NIHSS) (33), and comorbidities of patients. The 
CBAD was performed within the first two weeks after 
the acute ischaemic stroke in the area of carotid artery, 
and covered the following details: (1) anatomy and func-
tionality of oral structures, (2) feeding method, (3) de-
scription of oral and pharyngeal phases of swallowing, 
possible symptoms of impaired safety and/or efficacy of 
swallowing, and (4) detailed IDDSI diet level of food and 
liquid (34).
2.1.4 Raters
All raters were SLPs with more than 2 years of work-
ing experience in treating patients with dysphagia (2 to 
17 years of working experience, M=7.33 years). Their 
results were used to calculate interrater reliability. One 
skilled clinical SLP with 23 years of experience in treat-
ing dysphagia patients was evaluating the same 30 clin-
ical cases using both scales, IDDSI-FDS, and FOIS-SI. 
Those results were used to calculate convergent validity.
2.1.5 Interrater and intrarater reliability
The interrater reliability of FOIS-SI was obtained as a 
result of comparing the scores of six SLPs from different 
facilities across the country. Regardless of their famil-
iarity with the FOIS-SI scale, all raters received written 
instructions on how to evaluate the severity of dyspha-
gia using the translated scale. They were asked to assign 
each speech and language pathology report a FOIS rat-
ing between Level 1 and Level 7. Each rater was blinded 
to other raters’ evaluations.
To evaluate intrarater reliability, two SLPs evaluated 
the same 30 clinical cases on two occasions within an 
interval of 10-14 days. The cases were shuffled to ensure 
as objective assessment as possible.
2.1.6 Convergent validity
To evaluate convergent validity, we examined the 
association between FOIS-SI and IDDSI-Functional 
Diet Scale (IDDSI-FDS). The IDDSI-FDS was chosen 
according to CBAD recommendations on IDDSI diets 
(34), aiming to classify dysphagia severity based on sug-
gested diet modifications.
The IDDSI-FDS is a scale that can objectively capture 
oral dysphagia and texture restriction. Authors recom-
mend its use for paediatric and adult populations, es-
pecially where the IDDSI framework and its 8 levels of 
food and liquids consistency are used (28). One skilled 
clinical SLP evaluated 30 clinical cases separately, once 
with IDDSI-FDS and once with FOIS-SI.
2.1.7 Data gathering and statistical analysis
For gathering data, we used Microsoft® Excel®, 2016. 
All statistical analyses were performed using SPSS Statis-
tics, version 25, IBM® SPSS®.
To calculate reliability the Intraclass Correlation 
Coefficient (ICC) was used. A two-way random-effect 
model based on single ratings and absolute agreement 
assessed the interrater reliability, and a two-way mixed 
effect model based on single rating and absolute agree-
ment assessed the intrarater reliability for either rater. 
Interpretation was as follows: between 0.5 and 0.75, 
moderate; between 0.75 and 0.9, good; above 0.90, ex-
cellent agreement (35). Mean estimations along with a 
95% confidence interval (CI) were reported for the ICC. 
Convergent validity was calculated with the Spear-
man’s rank correlation coefficient, assuming that a κ of 
0.7 or more indicates a high positive correlation between 
two scales and more than 0.9 indicates a very high posi-
tive correlation (36).
3 Results
Of the 30 patients (age 72.23±1.73 years, ranging 
from 48 to 94 years), 7 were women and 23 were men 
(female to male ratio 1:3.29). The acute ischaemic stroke 
was located in the left carotid artery territory in 20 
patients and in the right carotid artery territory in 10 
patients. The most common pathologies found in the 
group of patients in the study were arterial hypertension 
(90%), hyperlipidaemia (70%), right-sided haemiparesis 
(56.67%), atrial fibrillation (40%), carotid artery stenosis 
(26.67%), and left-sided haemiparesis (20%). Regarding 
the NIHSS, the prevalent scores were severe (>13) in 15 
patients (50%), moderate (6-13) in 11 patients (36.67%), 
and mild (1-5) in 4 patients (13.33%). The severity of 
dysphagia was assessed with FOIS-SI (see Table 3).
The ICC was used to determine if there was an agree-
ment between the SLPs’ judgements of clinical cases on 
FOIS-SI. The results showed that the ICC for interrater 
Table 3: The severity of dysphagia among 30 patients with acute stroke in the carotid artery territory as assessed by 6 
raters using FOIS-SI. Additionally, 2nd ratings of two raters and one highly skilled SLP, who evaluated dysphagia using FOIS-
SI and IDDSI-FDS.
SLP 1 FOIS-SI 2 FOIS-SI 3 FOIS-SI 4 FOIS-SI 5 FOIS-SI 6 FOIS-SI Highly skilled SLP
Case 1st 
rating
2nd 
rating
1st 
rating
2nd 
rating
FOIS-SI IDDSI-FDS
1 1 1 1 1 1 1 1 1 1 0
2 5 5 5 5 6 6 5 5 5 5
3 5 5 5 5 5 5 6 6 5 6
4 5 5 5 5 4 4 5 5 5 5
5 1 2 1 1 1 1 1 1 1 0
6 5 5 5 5 5 5 5 5 5 6
7 2 2 2 2 3 3 2 2 2 0
8 5 5 5 5 4 4 4 4 5 5
9 5 5 5 5 4 4 5 5 5 5
10 5 5 5 5 5 5 6 5 5 6
11 5 5 5 5 4 4 5 6 5 5
12 5 5 5 5 4 4 5 5 5 5
13 5 5 5 5 5 5 5 5 5 6
14 6 6 6 6 6 6 6 6 6 7
15 2 1 2 2 2 2 1 1 2 0
16 4 4 4 4 4 4 4 4 4 1
17 1 1 1 1 1 1 1 1 1 0
18 5 5 5 5 5 5 5 5 5 6
19 1 1 1 1 1 1 1 1 1 0
20 6 6 6 6 6 6 5 5 6 7
21 4 4 4 4 4 4 4 4 4 1
22 5 5 6 5 6 6 6 6 5 7
23 5 5 5 5 5 5 5 5 5 6
24 7 7 7 7 7 7 7 7 7 8
25 5 5 4 5 5 5 5 5 5 3
26 1 1 1 1 1 1 1 1 1 0
27 2 2 2 2 1 1 2 2 2 0
28 4 4 4 4 4 4 4 4 4 1
29 4 4 4 4 4 4 4 4 4 1
30 6 6 6 5 6 6 6 6 5 7
Legend: SLP – speech and language pathologists; FOIS – Functional Oral Intake Scales; FOIS-SI – Slovenian translation of FOIS; 
IDDSI-FDS – Functional Diet Scale.
87
ORIGINAL SCIENTIFIC ARTICLE
Reliability and validity of the Slovenian Translation of the Functional Oral Intake Scale (FOIS-SI)
according to CBAD recommendations on IDDSI diets 
(34), aiming to classify dysphagia severity based on sug-
gested diet modifications.
The IDDSI-FDS is a scale that can objectively capture 
oral dysphagia and texture restriction. Authors recom-
mend its use for paediatric and adult populations, es-
pecially where the IDDSI framework and its 8 levels of 
food and liquids consistency are used (28). One skilled 
clinical SLP evaluated 30 clinical cases separately, once 
with IDDSI-FDS and once with FOIS-SI.
2.1.7 Data gathering and statistical analysis
For gathering data, we used Microsoft® Excel®, 2016. 
All statistical analyses were performed using SPSS Statis-
tics, version 25, IBM® SPSS®.
To calculate reliability the Intraclass Correlation 
Coefficient (ICC) was used. A two-way random-effect 
model based on single ratings and absolute agreement 
assessed the interrater reliability, and a two-way mixed 
effect model based on single rating and absolute agree-
ment assessed the intrarater reliability for either rater. 
Interpretation was as follows: between 0.5 and 0.75, 
moderate; between 0.75 and 0.9, good; above 0.90, ex-
cellent agreement (35). Mean estimations along with a 
95% confidence interval (CI) were reported for the ICC. 
Convergent validity was calculated with the Spear-
man’s rank correlation coefficient, assuming that a κ of 
0.7 or more indicates a high positive correlation between 
two scales and more than 0.9 indicates a very high posi-
tive correlation (36).
3 Results
Of the 30 patients (age 72.23±1.73 years, ranging 
from 48 to 94 years), 7 were women and 23 were men 
(female to male ratio 1:3.29). The acute ischaemic stroke 
was located in the left carotid artery territory in 20 
patients and in the right carotid artery territory in 10 
patients. The most common pathologies found in the 
group of patients in the study were arterial hypertension 
(90%), hyperlipidaemia (70%), right-sided haemiparesis 
(56.67%), atrial fibrillation (40%), carotid artery stenosis 
(26.67%), and left-sided haemiparesis (20%). Regarding 
the NIHSS, the prevalent scores were severe (>13) in 15 
patients (50%), moderate (6-13) in 11 patients (36.67%), 
and mild (1-5) in 4 patients (13.33%). The severity of 
dysphagia was assessed with FOIS-SI (see Table 3).
The ICC was used to determine if there was an agree-
ment between the SLPs’ judgements of clinical cases on 
FOIS-SI. The results showed that the ICC for interrater 
Table 3: The severity of dysphagia among 30 patients with acute stroke in the carotid artery territory as assessed by 6 
raters using FOIS-SI. Additionally, 2nd ratings of two raters and one highly skilled SLP, who evaluated dysphagia using FOIS-
SI and IDDSI-FDS.
SLP 1 FOIS-SI 2 FOIS-SI 3 FOIS-SI 4 FOIS-SI 5 FOIS-SI 6 FOIS-SI Highly skilled SLP
Case 1st 
rating
2nd 
rating
1st 
rating
2nd 
rating
FOIS-SI IDDSI-FDS
1 1 1 1 1 1 1 1 1 1 0
2 5 5 5 5 6 6 5 5 5 5
3 5 5 5 5 5 5 6 6 5 6
4 5 5 5 5 4 4 5 5 5 5
5 1 2 1 1 1 1 1 1 1 0
6 5 5 5 5 5 5 5 5 5 6
7 2 2 2 2 3 3 2 2 2 0
8 5 5 5 5 4 4 4 4 5 5
9 5 5 5 5 4 4 5 5 5 5
10 5 5 5 5 5 5 6 5 5 6
11 5 5 5 5 4 4 5 6 5 5
12 5 5 5 5 4 4 5 5 5 5
13 5 5 5 5 5 5 5 5 5 6
14 6 6 6 6 6 6 6 6 6 7
15 2 1 2 2 2 2 1 1 2 0
16 4 4 4 4 4 4 4 4 4 1
17 1 1 1 1 1 1 1 1 1 0
18 5 5 5 5 5 5 5 5 5 6
19 1 1 1 1 1 1 1 1 1 0
20 6 6 6 6 6 6 5 5 6 7
21 4 4 4 4 4 4 4 4 4 1
22 5 5 6 5 6 6 6 6 5 7
23 5 5 5 5 5 5 5 5 5 6
24 7 7 7 7 7 7 7 7 7 8
25 5 5 4 5 5 5 5 5 5 3
26 1 1 1 1 1 1 1 1 1 0
27 2 2 2 2 1 1 2 2 2 0
28 4 4 4 4 4 4 4 4 4 1
29 4 4 4 4 4 4 4 4 4 1
30 6 6 6 5 6 6 6 6 5 7
Legend: SLP – speech and language pathologists; FOIS – Functional Oral Intake Scales; FOIS-SI – Slovenian translation of FOIS; 
IDDSI-FDS – Functional Diet Scale.
88
NEUROLOGY, NEUROPSYCHOLOGY, NEUROPHYSIOLOGY
Zdrav Vestn | March – April 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3167
reliability was excellent being 0.959 (0.934-0.978).
Two SLPs (SLP 2 and SLP 6, see Table 3) evaluated 
30 clinical cases on two occasions. The second evalua-
tion was performed two weeks after the first one. The 
ICC for intrarater reliability was excellent being 0.979 
(0.957-0.990) and 0.991 (0.980-0.995) for rater 2 and 6, 
respectively.
One highly experienced SLP evaluated the same 
30 cases with the FOIS and the IDDSI-FDS in parallel 
(see Table 3). Spearman’s rank correlation coefficient 
was used to evaluate convergent validity. There was a 
very high positive correlation between FOIS-SI and 
IDDSI-FDS, which was statistically significant, rs=0.927, 
p=.0001.
4 Discussion
FOIS was initially developed for adult stroke patients 
(10). It has also been justified for the pediatric popula-
tion (11), and patients with other diseases (15-23). The 
FOIS was translated into different languages (German, 
Italian, Chinese), where psychometric studies showed 
FOIS to be a valid instrument for the evaluation of dys-
phagia (12-14). However, solely the German and the 
Chinese studies were comparable to ours since the Ital-
ian study had a different research perspective.
The purpose of the present paper was to translate and 
adapt the FOIS scale of functional severity of dysphagia 
in stroke patients and make this scale available to Slove-
nian clinicians and researchers across the country in all 
clinical and care settings. The study was not intended to 
determine the reliability of clinical bedside examination 
itself.
Enrolled SLPs evaluated 30 clinical records of stroke 
survivors. The patients had an ischemic stroke in the 
carotid artery territory. CBAD was performed by the 
time of patients’ acute phase after the stroke event. As 
far as reliability of the FOIS-SI is concerned, both in-
tra- and interrater reliability were analyzed. The ICC 
for interrater and intrarater reliability were both excel-
lent, the first being 0.959 and the second being 0.979 
and 0.991. Intrarater reliability value was similar (or 
greater) to those reported in the German study, where 
Fleiss kappa (κ=0.83) showed high agreement; Chinese 
study, where Cohen kappa showed excellent agreement 
(κ=0.881); and original English study, where an average 
kappa value ranged from 0.86 to 0.91. High reliability in 
these studies could be because raters received prior FOIS 
training (12), the study taking place at just a single facili-
ty (14), or the group of patients being more homogenous 
(10). There was no report about intrarater reliability in 
the aforementioned studies. Raters in our study were 
familiar with the FOIS-SI scale and received written in-
structions beforehand, which can potentially contribute 
to the excellent interrater and intrarater reliability. How-
ever, some discrepancies were found. The disagreements 
were mostly detected between FOIS Level 4 and 5 and 
between FOIS Level 2 and 3, where the insecurities were 
mostly about the different types of tubes and with the 
term single consistency (see Table 3).
In our study, the validity of the FOIS-SI was evaluat-
ed with the IDDSI-FDS theoretically related scale. The 
IDDSI-FDS scale was chosen since the IDDSI framework 
is slowly spreading both internationally and nationally. 
One highly skilled SLP evaluated the severity of dyspha-
gia with both, FOIS-SI and IDDSI-FDS. Results have 
shown a very high positive correlation between these 
two scales. To our knowledge, a study of the correlation 
between these two scales has not been performed yet. 
The German and Chinese studies, on the other hand, 
tested the validity of the translated FOIS scales with 
the stroke scales NIHSS and MRS and showed signifi-
cant correlation. Additionally, the German and Chinese 
studies correlated FOIS with the golden standards of di-
agnosis of swallowing disorders (FEES and VFSS) and 
found a significant association between the severity of 
dysphagia as assessed by these two methods. However, 
the Chinese study did not show a significant correlation 
of FOIS with aspiration (14), which was the case as well 
in the original FOIS study (10).
There is one major limitation in this study that could 
be addressed in future research. For convergent valida-
tion, we used IDDSI-FDS, which was, up to this point, 
only initially validated. For this reason, further vali-
dation studies using other scales or one of the golden 
standards for diagnosing swallowing problems, such as 
FEES or VFSS, should be used. However, the Chinese, 
German, and original study validated their FOIS scale 
not only with different dysphagia and stroke scales but 
also with the golden standards, which definitely con-
firmed FOIS to be a valid scale to evaluate the severity of 
dysphagia in stroke survivors.
Future studies should investigate, whether FOIS-SI 
can provide an accurate level of dysphagia severity in 
other groups of patients with dysphagia, and the respon-
siveness of the scale to SLP treatment.
5 Conclusion
This study was intended to determine the interrat-
er reliability across clinicians from different clinical 
institutes across the entire country, evaluate intrarater 
89
ORIGINAL SCIENTIFIC ARTICLE
Reliability and validity of the Slovenian Translation of the Functional Oral Intake Scale (FOIS-SI)
reliability, and determine the convergent validity of 
FOIS-SI.
The initial psychometric characteristics study implies 
that FOIS-SI could be a useful tool for various clinical 
and scientific purposes for quantifying the severity of 
dysphagia across the country and different facilities. 
Since stroke patients often get transferred to different 
hospitals or clinics due to change in the amount of care 
they require as their treatment progresses, utilizing a 
standardized model between hospitals, clinics, and care 
settings can contribute to better dysphagia outcomes as 
well as to a higher quality of life in dysphagia patients.
Conflict of interest
None declared.
Acknowledgments
The authors would like to express their gratitude to 
the speech and language pathologists involved in this 
study.
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