RESEARCH ARTICLE Open Access
Fac o s associa ed wi h a i ion in a
longi udinal online s udy: esul s om he
HaBIDS panel
Nicole Rübsamen
1,2
, Manas K. Akma o
1,3,4
, S e anie Cas ell
1,3
, And é Ka ch
1,2
and Ra ael T. Mikolajczyk
1,5,6*
Abs ac
Backg ound: Knowing abou p edic o s o a i ion in a panel is impo an o ini ia e ea ly measu es agains loss o
pa icipan s. We in es iga ed a i ion in bo h ea ly and la e phase o an online panel wi h special ocus on p e e ences
ega ding mode o pa icipa ion.
Me hods: We used da a om he HaBIDS panel ha was designed o in es iga e knowledge, a i udes, and p ac ice
ega ding in ec ions in he Ge man gene al popula ion. HaBIDS was di ided in o wo phases: an ini ial phase when
some pa icipan s could choose hei p e e ed mode o pa icipa ion (pape -and-pencil o online) and an ex ended
phase when pa icipan s we e asked o become membe s o an online panel ha was no limi ed ega ding
i s du a ion (i.e. pa icipan s ini ially p e e ing pape ques ionnai es swi ched o online pa icipa ion). Using
compe ing isks eg ession, we in es iga ed wo ypes o a i ion ( o mal wi hd awal and discon inua ion
wi hou wi hd awal) among online pa icipan s, sepa a ely o bo h phases. As po en ial p edic o s o a i ion,
we conside ed sociodemog aphic cha ac e is ics, physical and men al heal h as well as auxilia y in o ma ion
desc ibing he su ey p ocess, and, in he ex ended phase, ini ial mode p e e ence.
Resul s: In he ini ial phase, highe age and less equen In e ne usage p edic ed wi hd awal, while younge age, highe
s ess le els, delay in e u ning he consen o m, and need o ecei ing eminde emails p edic ed discon inua ion. In he
ex ended phase, only need o ecei ing eminde emails p edic ed discon inua ion. Numbe s o wi hd awal in
he ex ended phase we e oo small o analysis. Ini ial mode p e e ence did no p edic a i ion in he ex ended
phase. Besides age, he e was no e idence o di e en ial a i ion by sociodemog aphic ac o s in any phase.
Conclusions: P edic o s o a i ion we e simila in bo h phases o he panel, bu hey di e ed by ype o a i ion
(wi hd awal s. discon inua ion). Sociodemog aphic cha ac e is ics only played a mino ole o bo h ypes o
a i ion. Need o ecei ing a eminde was he s onges p edic o o discon inua ion in any phase, bu no
p edic o o wi hd awal. We ound p edic o s o a i ion, which can be iden i ied al eady in he ea ly phase o a
panel so ha coun e measu es (e.g. special incen i es) can be aken.
Keywo ds: A i ion, Heal h su ey, In e ne , Longi udinal s udy, Mixed-mode, Online, Panel, Pa icipa ion,
Response, Wi hd awal
* Co espondence: [email p o ec ed]
1
Depa men o Epidemiology, Helmhol z Cen e o In ec ion Resea ch (HZI),
Inho ens aße 7, 38124 B aunschweig, Ge many
5
Hanno e Medical School, Hanno e , Ge many
Full lis o au ho in o ma ion is a ailable a he end o he a icle
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Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132
DOI 10.1186/s12874-017-0408-3
Backg ound
In 2005, Eysenbach a gued ha a “science o a i ion”
is needed [1]. He dis inguished wo ypes o a i ion in
he con ex o in e en ional eHeal h applica ions:
use s who o mally wi hd aw and use s who do no
o mally wi hd aw, bu who a e no longe using he
applica ion (discon inua ion). Eysenbach s a es ha
hese ypes o a i ion can ei he be closely ela ed o
no , i.e. ha i is possible o ha e low a es o wi h-
d awal, bu s ill many pa icipan s no using he appli-
ca ion (he ci es [2, 3] as examples). He hypo hesized
ha a high p opo ion o wi hd awal is a esul o dis-
con inua ion. Following Eysenbach, se e al au ho s
ha e in es iga ed he ypes o a i ion in eHeal h in-
e en ions [4–7]. Howe e , since eHeal h in e en-
ions a e mos ly ailo ed o he indi idual pa icipan ,
hei indings abou a i ion migh no be ans e able
o online panels (which do no include indi idualized
in e en ions).
In online panels, he p oblem o a i ion was s udied
in he con ex o social and poli ical sciences [8–10],
showing ha sociodemog aphic ac o s as well as o he
ac o s possibly changing o e ime, e.g. commi men
o he su ey o panel a igue, we e associa ed wi h a -
i ion [8]. Da a on a i ion in heal h- ela ed online
panels is es ic ed o speci ic esea ch ields, e.g. syn-
d omic su eillance [11] o changes in heal h among
adolescen s [12]. I is no clea i p edic o s o a i ion
in heal h- ela ed online panels a e compa able o hose
in panels in he con ex o social sciences. Knowing
who is a isk o a i ion in a panel is impo an o
make e o s o keep hose pa icipan s a isk engaged
in hepaneland obeable op edic biasaspanela -
i ion can limi gene alizabili y and make analyses o
epea ed ( ollow-up) measu emen s mo e complica ed
and less alid [7].
Wi h inc easing use o he in e ne , s udies using
online da a collec ion, especially wi h mobile applica-
ions, will likely become mo e common in u u e;
s ill i is no clea i hose who would –gi en he
choice –p e e o he modes o pa icipa ion display
dis inc pa e ns o a i ion when pa icipa ing in an
online panel.
We ook ad an age o da a om a longi udinal panel
on heal h- ela ed issues and in es iga ed wo ques ions:
1) which ac o s a e associa ed wi h su ey a i ion, and
2) i a i ion di e s be ween hose who ini ially pa ici-
pa ed in he panel by pape -and-pencil and ag eed o
swi ch o online pa icipa ion la e and hose who pa ic-
ipa ed online om he beginning. We di e en ia ed
be ween wi hd awal and discon inua ion because we hy-
po hesized ha hese wo en i ies ep esen di e en
g oups o pa icipan s ha ha e di e en easons o s op
pa icipa ing in he s udy.
Me hods
Rec ui men
This analysis was based on he popula ion-based, longi-
udinal Hygiene and Beha iou In ec ious Diseases S udy
(HaBIDS), conduc ed in ou egions o Lowe Saxony,
Ge many and designed o assess knowledge, a i udes,
and p ac ice ela ed o in ec ious diseases and o in es i-
ga e e ec s o su ey design [13, 14]. Po en ial pa ici-
pan s be ween 15 and 69 yea s o age we e d awn by
means o p opo ional s a i ied andom sampling om
he egional popula ion egis ies. We sampled indi id-
uals p opo ionally om 22 age-sex s a a (11 age g oups
mul iplied by wo sexes). We did no explici ly aim o
include o exclude immig an s, bu only included he
ac ion o immig an s ha li ed in he s udy egions a
he ime o sampling. Pa icipan s in he s udy we e
asked i hey we e bo n in Ge many. We did no include
a ques ion abou i s o second deg ee immig a ion.
In a i s wa e (Janua y 2014), we used a mixed-mode
app oach, i.e. we o e ed a choice be ween pape -and-
pencil and online pa icipa ion o 16,895 po en ial pa -
icipan s li ing in he egions B aunschweig and Vech a.
We e e o indi iduals who chose pape -and-pencil pa -
icipa ion as “mixed-mode: pape ”g oup and o indi id-
uals who chose online pa icipa ion as “mixed-mode:
online”g oup (Table 1 gi es an o e iew o he g oups
de ined h oughou his a icle). In a second wa e (Ap il
2014), we o e ed only online pa icipa ion o 10,000
newly in i ed po en ial pa icipan s li ing in Salzgi e
and Wol enbü el. We e e o pa icipan s om his
second wa e as “online-only”g oup. All po en ial pa ic-
ipan s ecei ed one in i a ion le e ia land mail and no
u he eminde le e s. To s imula e con inuing pa ici-
pa ion, we o e ed bimon hly eedbacks abou esul s o
he s udy.
S udy phases
We s a ed in he in i a ion le e o he HaBIDS s udy
ha he s udy would consis o nine online o wo
pape -and-pencil ques ionnai es, i.e. ha he s udy
would be limi ed ega ding i s du a ion. Be ween Janua y
2014 and July 30 h, 2015 (“ini ial phase”), online pa ici-
pan s, i.e. pa icipan s in “mixed-mode: online”and “on-
line-only”, ecei ed ques ionnai es A o K (Addi ional
ile 1 illus a es he iming, leng h, opics, and esponse
a es o all ques ionnai es; Addi ional ile 2 p o ides he
English ansla ion o all ques ionnai es). The “online-
only”pa icipan s ecei ed ques ionnai es A and B a
he same ime o compensa e o hei delayed ec ui -
men in o he panel. The “mixed-mode: pape ”pa ici-
pan s ecei ed wo pape ques ionnai es: he i s one
included he opics A, B, C, D and he second one in-
cluded E, G, H, I, K. Ques ionnai es F and J we e sen o
online pa icipan s only because hey we e added in he
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 2 o 11
cou se o he s udy o su ey pa icipan s abou ecen
opics (Ebola, In luenza).
In an ex ended phase s a ing on July 30 h, 2015, we
in i ed all pa icipan s o he ini ial phase (who had no
o mally wi hd awn so a ) o con inue wi h he s udy
and become pa o he HaBIDS online panel ha was
no limi ed ega ding i s du a ion. In i a ion o his ex-
ended phase s a ed ha new ques ionnai es would be
sen o panel membe s e e y wo o h ee mon hs. Fo
“mixed-mode: pape ”pa icipan s, becoming pa o his
online panel mean o swi ch he mode o pa icipa ion.
I a pa icipan did no wan o become pa o he
HaBIDS online panel, we asked abou he easons o
his decision in a mul iple choice ques ion. All panel
membe s ecei ed i e ques ionnai es (ques ionnai e L
o P, Addi ional ile 1) be ween Augus 2015 and May
2016.
Fo each online ques ionnai e (A o P), we sen a sin-
gle eminde (email) o pa icipan s who had no illed
in he ques ionnai e wi hin wo weeks a e he ini ial in-
i a ion. In each email ha he pa icipan s ecei ed (in-
i a ions o ques ionnai es as well as eminde emails),
pa icipan s we e old explici ly ha i hey wish, hey
can wi hd aw om he s udy and u he eminde s by
eplying o he email.
A low diag am ha summa izes ec ui men p ocess
and s udy phases is p esen ed in Addi ional ile 3.
Resea ch ques ions
Figu e 1 p esen s an o e iew o ou esea ch ques ions,
on which we elabo a e below.
Ou i s aim was o in es iga e which ac o s a e asso-
cia ed wi h su ey a i ion. We we e especially in e -
es ed in in es iga ing i he same a iables we e
associa ed wi h a i ion in bo h he ea ly and he la e
phase o an online panel. I hey would di e , hen i
would be ad isable o ailo coun e measu es, e.g. special
incen i es, o he di e en phases o an online panel. We
in es iga ed (1a) which ac o s a e associa ed wi h a i-
ion in he ini ial phase o he online panel and (1b)
which ac o s a e associa ed wi h a i ion in he ex-
ended phase o he online panel.
Ou second aim was o in es iga e i a i ion di e s
be ween hose who ini ially pa icipa ed in he s udy by
pape -and-pencil and ag eed o swi ch o online pa ici-
pa ion la e , and hose who pa icipa ed online om he
beginning. To assess i he e is selec ion bias in he ex-
ended phase, we in es iga ed i pa icipan s wi h ce ain
sociodemog aphic cha ac e is ics we e less likely o be
ans e ed om he ini ial s udy o he online panel.
We in es iga ed (2a) which ini ial pape -and-pencil pa -
icipan s ag ee o con inue wi h he online panel, (2b)
which ini ial online pa icipan s ake pa in he ex-
ended phase and (2c) i a i ion in he online panel di -
e s be ween hose who ini ially op ed o pape -and-
pencil ques ionnai es compa ed o hose who op ed o
online pa icipa ion.
De ini ion o a i ion
We di ided he online pa icipan s in he ini ial phase as
well as he online panel membe s in he ex ended phase
in o h ee mu ually exclusi e ou come g oups: wi h-
d awe s ( hose who o mally e oked hei pa icipa ion),
discon inue s ( hose who did no ill in a leas wo con-
secu i e ques ionnai es and emained non- esponde ; see
o Addi ional ile 4 ha illus a es discon inua ion), and
egula use s (pa icipan s who nei he wi hd ew no dis-
con inued pa icipa ion). Acco ding o he me hod p o-
posed by Eysenbach [1], we es ic ed he in es iga ed
g oups o hose pa icipan s who had illed in he i s
ques ionnai e o he co esponding phase, i.e. ques ion-
nai e A o AB in he ini ial phase and ques ionnai e L in
he ex ended phase, espec i ely.
Table 1 De ini ion o exp essions used h oughou he a icle
Exp ession De ini ion
Phase 1:
Ini ial phase
S udy phase be ween ini ial in i a ion o he
HaBIDS panel and in i a ion o he imely
unlimi ed panel (includes ques ionnai es A o K)
“Mixed-mode:
pape ”g oup
g oup o indi iduals who chose o pa icipa e
ia pape -and-pencil ques ionnai es in he
mixed-mode su ey
“Mixed-mode:
online”g oup
g oup o indi iduals who chose o pa icipa e
ia online ques ionnai es in he mixed-mode
su ey
“Online-only”
g oup
g oup o indi iduals who pa icipa e in he
online-only su ey (pa icipa ion only possible
ia online ques ionnai es)
Ini ial online
pa icipan s
g oup o indi iduals who pa icipa e ia online
ques ionnai es in bo h su eys, i.e. union o he
wo g oups “mixed-mode: online”and
“online-only”
Phase 2:
Ex ended phase
(online panel)
S udy phase be ween in i a ion o he imely
unlimi ed panel and la es ques ionnai e
(includes ques ionnai es L o P)
Fo me pape
pa icipan s
“mixed-mode: pape ”who con inued
pa icipa ing in he ex ended phase,
i.e. who swi ched om pa icipa ion ia
pape -and-pencil o online
ques ionnai es
All- ime online
pa icipan s
online pa icipan s who con inued pa icipa ing
in he ex ended phase
Bo h phases
Wi hd awe s pa icipan s who o mally wi hd aw om HaBIDS
Discon inue s pa icipan s who do no o mally wi hd aw, bu
who a e no longe illing in ques ionnai es
( his condi ion is ul illed i a leas wo consecu i e
ques ionnai es a e missing and he pa icipan does
no e u n o he s udy; see o Addi ional ile 4 ha
illus a es discon inua ion)
Regula use s pa icipan s who nei he wi hd aw no discon inue
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 3 o 11
The da e o wi hd awal was de ined as he da e o
in i a ion o he ques ionnai e in ela ion o which
wi hd awal was decla ed. The da e o discon inua ion
was de ined as he da e o in i a ion o he i s ques-
ionnai e ha was no illed in. In ew cases, email
deli e y ailed a some poin du ing he s udy so ha
pa icipan s did no longe ecei e in i a ion emails. In
hese cases, he pa icipan was excluded comple ely
om he analyses o he espec i e phase, i.e. ini ial
o ex ended phase.
P edic o s o a i ion
As po en ial p edic o s o a i ion, we conside ed socio-
demog aphic cha ac e is ics, sel - epo ed physical and
men al heal h as well as me ada a (auxilia y in o ma ion
desc ibing he su ey p ocess). Sociodemog aphic cha -
ac e is ics comp ised age, sex, ma i al s a us (ma ied,
unma ied, di o ced, widowed), highes comple ed edu-
ca ional le el (lowe seconda y educa ion o app en ice-
ship, s ill a uppe seconda y school, uni e si y en ance
quali ica ion [ h ough uppe seconda y educa ion o o-
ca ional school], and uni e si y deg ee), and equency
o In e ne usage (daily and less han daily).
Da a abou physical and men al heal h included sel -
a ed heal h s a us (excellen , e y good, good, ai , poo )
[15], WHO-5 well-being index (sum o i e i ems, sco e
anges om 0 [poo well-being] o 100 [excellen well-
being]) [16], pe cei ed s ess scale (PSS, mean o ou
S ill pa icipa ing
a he ime o analysis
Pa icpa ing
in he ex ended phase
S ill pa icipa ing a he
end o he ini ial phase
Pa icipa ing
in he ini ial phase
A i ion
in he
in ial
phase
Swi ching
modes
A i ion
in he
ex ended
phase
(2a)
Which ini ial pape -and-pencil
pa icipan s ag ee o con inue
wi h he online panel?
(2b)
Which ini ial online pa icipan s
ake pa in he ex ended phase?
(2c)
Does a i ion in he online panel
di e be ween hose who ini ially
op ed o pape -and-pencil
ques ionnai es compa ed o hose
who op ed o online pa icipa ion?
(1b)
Which ac o s a e associa ed
wi h a i ion in he ex ended phase
o he online panel?
Ini ial phase
(ques ionnai es A o K,
Janua y 2014 o July 2015)
In i a ion o con inue
wi h he panel
(pape -and-pencil pa icipan s
swi ch o online mode)
Ex ended phase
(ques ionnai es L o P,
Augus 2015 o May 2016)
(1a)
Which ac o s a e associa ed
wi h a i ion in he ini ial phase
o he online panel?
Aims
1. To in es iga e which ac o s a e associa ed wi h su ey a i ion
2. To in es iga e i a i ion di e s be ween hose who ini ially pa icipa ed in he panel
by pape -and-pencil and ag eed o swi ch o online pa icipa ion la e and hose who
pa icipa ed online om he beginning
Fig. 1 O e iew o he esea ch ques ions
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 4 o 11
i ems, sco e anges om 0 [ e y low s ess le el] o 16
[ e y high s ess le el]) [17], and mean sco e based on
in ec ions and in ec ion-associa ed symp oms in he las
12 mon hs (“ID Sc een”, sco e anges om 0 [no in ec-
ions in he las 12 mon hs] o 46 [mo e han 42 in ec-
ions in he las 12 mon hs]) [18].
Me ada a included ini ially p e e ed mode o pa ici-
pa ion (online e sus pape -and-pencil), ime be ween
in i a ion and e u n o he signed in o med consen
o m (in days), and whe he he pa icipan esponded
only a e ecei ing a eminde email o he i s online
ques ionnai e (i.e. ques ionnai e A in he ini ial phase
and ques ionnai e L in he ex ended phase). We only
looked a he need o eminde s o he i s ques ion-
nai e o in es iga e i al eady a his ime poin la e a -
i ion can be p edic ed.
In he analysis o po en ial sel -selec ion in o he ex-
ended phase (ques ions 2a and 2b), we also conside ed
numbe o ques ionnai es illed in du ing he ini ial
phase and o al numbe o eminde s ecei ed du ing
he ini ial phase.
S a is ical analysis
We compa ed he s udy popula ion’s composi ion wi h
he a ge popula ion’s (inhabi an s o Lowe Saxony be-
ween 15 and 69 yea s o age [19]) composi ion by di id-
ing each popula ion in s a a o age, sex, and educa ion
and calcula ing he ac ion o each s a um in he e-
spec i e popula ion o assess he possibili y o gene a ing
gene alizable es ima es ia pos -s a i ica ion.
To answe ques ion 1a, we analysed da a om he ini-
ial phase in h ee s eps. To in es iga e how p edic o s
we e associa ed wi h each ype o a i ion, we build sep-
a a e Cox p opo ional haza ds eg ession models o
ob ain unadjus ed haza d a ios (sepa a ely o discon-
inua ion and wi hd awal) [20]. To make conclusions on
cumula i e isks, we hen applied compe ing isks e-
g ession [21] in combina ion wi h he leas absolu e
sh inkage and selec ion ope a o me hod (LASSO) o
simul aneously selec p edic o a iables and es ima e
eg ession pa ame e s [22]. We buil wo models (R
package “c p”) o in es iga e i p edic o s di e ed by
ype o a i ion: model A included discon inua ion as
e en o in e es and wi hd awal as compe ing e en
while model B included wi hd awal as e en o in e es
and discon inua ion as compe ing e en . As uning pa -
ame e , we used he λ ha minimized BIC (as desc ibed
in [22]). We compa ed models A and B ega ding he se-
lec ed a iables. Finally, i a p edic o a iable was se-
lec ed in bo h model A and B, bu he associa ions had
opposi e di ec ions o he wo ypes o a i ion, we
used a nonpa ame ic es o end ac oss o de ed
g oups [23] o in es iga e he o e all associa ion be ween
his p edic o a iable and he composi e endpoin (a -
i ion because o wi hd awal o discon inua ion).
To answe ques ion 2a and 2b, we applied he LASSO
in logis ic eg ession (R package “glmne ”, dependen
a iable = pa icipa ion in he ex ended phase) o he
subse o pape -and-pencil o online pa icipan s, e-
spec i ely (models C and D).
Fo answe ques ions 1b and 2c, we applied he
LASSO o da a om he ex ended phase. As only ew
pa icipan s wi hd ew du ing his phase, we used he
LASSO in Cox eg ession (R package “glmne ”) wi h dis-
con inua ion as dependen a iable (model E) and ex-
cluded pa icipan s who had wi hd awn. To accoun o
he e ec ha all- ime online pa icipan s we e al eady
used o online ques ionnai es, we used he χ
2
es o
compa e discon inua ion among he o me pape -and-
pencil pa icipan s be ween ques ionnai es L and P and
among he “online-only”pa icipan s (who we e also
“ o ced” o use he online mode) be ween ques ionnai es
A and E.
We conduc ed comple e-case analyses and conside ed
p≤0.05 as signi ican . To check he p opo ional haz-
a ds assump ion, we plo ed Schoen eld esiduals p io
o Cox and compe ing isks eg essions. To assess pos-
sible nonlinea i y o con inuous p edic o s, we es ima ed
ac ional polynomials p io o all eg ession analyses
[24]. By including all possible p edic o s in he LASSO,
we con olled o con ounding because he LASSO
e ained all p edic o s ha we e somehow associa ed
wi h he ou come. We did no conside in e ac ions in
he models. S a is ical analyses whe e pe o med in S a a
e sion 12 (S a aCo p LP, College S a ion, TX, USA [25])
and R Founda ion o S a is ical Compu ing ( e sion
3.3.3).
Resul s
A i ion among he online pa icipan s in he ini ial
phase (ques ion 1a)
O e all, 2379 (8.9%) o he in i ed indi iduals consen ed
o pa icipa e in HaBIDS (935 pa icipan s in “mixed-
mode: pape ”g oup, 750 in “mixed-mode: online”, and
694 in “online-only”). Compa ison o he s udy popula-
ion’s composi ion wi h he a ge popula ion’s (inhabi-
an s o Lowe Saxony be ween 15 and 69 yea s o age)
composi ion showed ha all s a a de ined by age, sex,
and educa ion we e occupied in HaBIDS (Addi ional ile
5). Among 2379 pa icipan s, only 109 (4.6%) had no
been bo n in Ge many.
Da a o 1127 online pa icipan s we e used in he ana-
lysis o a i ion in he ini ial phase ( he emaining 317
online pa icipan s did no ill in he i s online ques-
ionnai e). One i h o he ini ial online pa icipan s
(18.3%, n= 206) discon inued pa icipa ion while 6.3%
(n= 71) o mally wi hd ew om he s udy, bo h du ing
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 5 o 11

he ini ial phase o HaBIDS. Fo 0.9% (n= 10), email de-
li e y ailed a some poin du ing he ini ial phase. The
emaining 74.5% (n= 840) we e classi ied as egula
use s. Figu e 2 shows he cumula i e incidence
unc ions.
Among all p edic o s, only age showed s a is ically sig-
ni ican , uni a iable associa ions wi h bo h ypes o a i-
ion (Table 2).
The LASSO in compe ing isks eg ession (Table 3)
selec ed highe age and less equen In e ne usage as
p edic o s o wi hd awal; and younge age, highe PSS,
delay in e u ning he consen o m, and ecei ing e-
minde emails as p edic o s o discon inua ion.
The associa ions be ween age and he ou come had
opposi e di ec ions o he wo ypes o a i ion. We
ound ha he e was a end ac oss age g oups, wi h
30.0% o he younges pa icipan s (15 o 19 yea s) and
9.9% o he oldes pa icipan s (65 o 69 yea s) lea ing
he panel by wi hd awal o discon inua ion (Table 4,
p< 0.001 o end).
T ans e o pa icipan s o he HaBIDS online panel
(ques ions 2a and 2b)
O 748 pape -and-pencil pa icipan s and 1319 ini ial
online pa icipan s who had been in i ed o he ini ial
HaBIDS online panel ( he emaining 312 pa icipan s
had o mally wi hd awn so a ), 335 (44.8%) pape -and-
pencil pa icipan s and 702 (53.2%) ini ial online pa ici-
pan s consen ed o become imely unlimi ed panel
membe s. The main easons (in uni a iable analysis) o
no pa icipa ing in he ex ended phase we e “no ime”
(12.9% o all non-pa icipan s; mul iple choice was
possible), “no access o he In e ne ”(8.2%), “ oo many
ques ionnai es pe yea ”(6.4%), and “no in e es ”(5.0%).
Fo pape -and-pencil pa icipan s, he LASSO in logis-
ic eg ession selec ed lowe PSS sco e, highe ID-
Sc een, and ha ing e u ned bo h pape -and-pencil
ques ionnai es du ing he ini ial phase ins ead o only
one as p edic o s o ag eeing o con inue wi h online
pa icipa ion (Table 5). Fo ini ial online pa icipan s,
he LASSO selec ed inc easing age, being unma ied,
lowe PSS sco e, highe WHO-5 and ID-Sc een sco es,
delay in e u ning he consen o m, numbe o e u ned
ques ionnai es, and inc easing o al numbe o eminde
emails du ing he ini ial phase as p edic o s o con inued
pa icipa ion (Table 5).
A i ion in he ex ended phase (ques ions 1b and 2c)
Mo e han one hi d (37.3%, n= 125) o he o me
pape -and-pencil pa icipan s did no ill in he i s on-
line ques ionnai e a e hei ag eemen o con inue wi h
he ex ended phase (i.e. ques ionnai e L) compa ed o
11.0% o he all- ime online pa icipan s (n= 77,
p< 0.001 o he compa ison). Only h ee pa icipan s
wi hd ew du ing he ex ended phase; hese pa icipan s
we e excluded om he ollowing analyses. Among all
pa icipan s who illed in ques ionnai e L (n= 835), a -
i ion in he ex ended phase was nea ly equal be ween
o me pape -and-pencil pa icipan s and all- ime online
pa icipan s (5.7% s. 5.8%, espec i ely, p= 0.91) (Fig.
3). A i ion was highe among he “online-only”pa ici-
pan s a e he i s i e online ques ionnai es o he ini-
ial phase (AB o E) compa ed o a i ion among he
o me pape -and-pencil pa icipan s in he ex ended
phase (12.4% s. 5.7%, espec i ely, p= 0.004).
Fig. 2 Cumula i e incidence cu es o discon inua ion and wi hd awal among he online pa icipan s in he ini ial phase
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 6 o 11
The LASSO in Cox eg ession selec ed younge age
and ecei ing eminde emails as p edic o s o discon-
inua ion (Table 6).
Discussion
We in es iga ed a i ion in a longi udinal panel abou
heal h and ound simila p edic o s o a i ion in di e -
en phases o he su ey; howe e , he p edic o s di e ed
by ype o a i ion (wi hd awal s. discon inua ion).
Need o sending a eminde was he s onges p edic o
o discon inua ion, bu no p edic o o wi hd awal.
Sociodemog aphic cha ac e is ics only played a mino
ole o bo h ypes o a i ion.
To ou knowledge, he HaBIDS panel is he i s s udy
o in es iga e a i ion in di e en phases o a panel. The
need o sending a eminde was he s onges p edic o
o discon inua ion in he ini ial as well as in he
ex ended phase. I s e ec size was e en la ge in he ex-
ended (HR 4.20) han in he ini ial phase (HR 1.44).
This di e ence be ween phases could be caused by
changes in gene al ac o s like commi men , habi s, and
panel a igue (desc ibed by Lug ig [8]). Lug ig claims
ha commi men is especially impo an in he s a ing
phase o a longi udinal s udy when some pa icipan s
a e no eally con inced o he s udy. I pa icipa ion i -
sel , i.e. illing in he i s ques ionnai es, does no
change hei commi men quickly, hese pa icipan s a e
likely o discon inue ea ly. Gill e al. [6] also obse ed
he impo ance o commi men in hei online mon hly
dep ession esc eening p og am o simila leng h as ou
s udy and wi h sho ques ionnai es e e y mon h. Ou
analyses showed ha he need o ecei ing a eminde
o he i s ques ionnai e p edic s a i ion a la e ques-
ionnai es (Gill e al. did no send eminde emails, so
Table 2 Uni a iable haza d a ios o each ype o a i ion in he ini ial phase
Discon inua ion Wi hd awal
HR (95% CI) p- alue HR (95% CI) p- alue
Age a baseline (pe 10 yea s inc ease) 0.81 (0.73, 0.89) <0.001 1.24 (1.04, 1.47) 0.02
Sex
Male Re e ence Re e ence
Female 0.91 (0.69, 1.21) 0.54 0.84 (0.52, 1.34) 0.46
Ma i al s a us
Ma ied Re e ence Re e ence
Unma ied 1.32 (0.97, 1.79) 0.08 0.72 (0.41, 1.28) 0.26
Di o ced/widowed 1.18 (0.73, 1.93) 0.50 0.88 (0.38, 2.06) 0.77
Highes comple ed educa ional le el
Lowe seconda y educa ion o app en iceship 1.41 (0.52, 3.84) 0.50 2.44 (0.58, 10.31) 0.22
S ill a uppe seconda y school 0.89 (0.62, 1.29) 0.54 1.56 (0.89, 2.76) 0.12
Uni e si y en ance quali ica ion 1.13 (0.81, 1.56) 0.48 1.07 (0.59, 1.95) 0.82
Uni e si y deg ee Re e ence Re e ence
F equency o In e ne usage
Daily Re e ence Re e ence
Less han daily 1.23 (0.91, 1.67) 0.19 2.03 (1.26, 3.27) 0.004
Sel - a ed heal h s a us
Fai /poo 0.93 (0.55, 1.59) 0.80 1.57 (0.67, 3.68) 0.30
Good 1.09 (0.81, 1.47) 0.56 1.73 (1.03, 2.92) 0.04
Excellen / e y good Re e ence Re e ence
WHO-5 well-being index (pe 10 poin s inc ease) 0.96 (0.89, 1.03) 0.24 0.96 (0.85, 1.09) 0.57
PSS sco e (pe 1 poin inc ease) 1.07 (1.02, 1.12) 0.002 0.97 (0.89, 1.05) 0.46
ID-Sc een (pe 1 poin inc ease) 1.03 (0.99, 1.07) 0.10 1.01 (0.95, 1.08) 0.73
Time be ween in i a ion and e u n
o he illed in o med consen o m (pe week)
1.1 (1.04, 1.17) <0.001 0.98 (0.82, 1.16) 0.78
Had o be eminded o ill in he i s online ques ionnai e (A)
Yes 1.85 (1.27, 2.7) 0.001 0.82 (0.33, 2.05) 0.68
No Re e ence Re e ence
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 7 o 11
we un o una ely canno assess his obse a ion in hei
s udy). The need o ecei ing a eminde migh be in lu-
enced by commi men , bu also by ime cons ain s o
he pa icipan .
A e se e al ques ionnai es, pa icipa ion may ha e
become a habi , and pa icipan s do no longe con-
sciously hink abou he decision o espond, “bu pa -
icipa e because hey ha e done so all along”[8]. Lug ig
claims ha “once his habi is b oken, he esponden is
subsequen ly a a highe isk o […] a i ing”[8]. Con-
sen o con inue wi h he online panel in he ex ended
phase was associa ed wi h he numbe o p io ques ion-
nai es illed in. This could be a p oxy o commi men as
well as o habi (based on he pa icipan s esponse be-
ha iou , we canno dis inguish hese wo ac o s) and
highligh s again he impo ance o hese ac o s in a lon-
gi udinal panel.
Discon inua ion in he imely unlimi ed HaBIDS on-
line panel did no di e by p e ious mode o pa icipa-
ion. Howe e , he pe cen age o o me pape -and-
pencil pa icipan s who did no e en ill in he i s on-
line ques ionnai e in he online panel was highe han
among all- ime online pa icipan s. Those pa icipan s
who would gene ally ag ee o pa icipa e online, bu a e
no used o online da a collec ion o use he In e ne
e y i egula ly, p obably d op ou a he i s a emp .
Thus, amilia i y wi h he In e ne migh be a mo e im-
po an ac o o pa icipa ion in an online panel han a
ue mode p e e ence because un amilia i y wi h he
In e ne likely leads o a choice o pape -and-pencil
mode when his is o e ed.
Pa icipan s no using he In e ne daily had a
highe isk o wi hd awal, bu no a highe isk o
discon inua ion. One explana ion could be ha in e-
quen In e ne use s a e mo e selec i e in hei on-
line ac i i ies and a he p e e o wi hd aw i hey
do no like a s udy. Olde pa icipan s we e mo e
likely o wi hd aw han younge ones, bu less likely
o become discon inuous use s. O e all, olde pa ici-
pan s le he s udy less o en han younge ones.
The o me migh be mo e conscien ious so ha hey
a he wi hd aw i hey ha e no mo e ime o in e es
han discon inue wi hou any eedback o he e-
sea che s. Younge pa icipan s migh be busie o
ge mo e spam emails han olde ones, which migh
esul in discon inua ion ins ead o o mal wi h-
d awal. This is also e lec ed by he highe isk o
discon inua ion among pa icipan s wi h highe s ess
le els (highe PSS sco es).
Table 3 Fac o s associa ed wi h isk o a i ion among he online pa icipan s in he ini ial phase
Model A:
discon inua ion as e en o in e es ,
wi hd awal as compe ing e en
Model B:
wi hd awal as e en o in e es ,
discon inua ion as compe ing e en
Be a Haza d a io Be a Haza d a io
Age a baseline (pe 10 yea s inc ease) −0.15 0.86 0.10 1.11
F equency o In e ne usage no selec ed in his model
Daily Re e ence Re e ence
Less han daily 0.28 1.32
PSS sco e (pe 1 poin inc ease) 0.04 1.04 no selec ed in his model
Time be ween in i a ion and e u n
o he illed in o med consen o m
(pe week)
0.05 1.05 no selec ed in his model
Had o be eminded o ill in
he i s online ques ionnai e (A)
no selec ed in his model
Yes 0.37 1.44
No Re e ence
Va iables we e selec ed using he leas absolu e sh inkage and selec ion ope a o me hod in compe ing isks eg ession
PSS: pe cei ed s ess scale (sco e anges om 0 [ e y low s ess le el] o 16 [ e y high s ess le el])
Table 4 Associa ion be ween age and he composi e endpoin
(a i ion because o wi hd awal o discon inua ion) in he ini ial
phase
Age g oup (yea s) Pa icipan s lea ing he panel in he ini ial phase by
wi hd awal o discon inua ion
15–19 12 (30.0%)
20–24 21 (28.4%)
25–29 21 (21.0%)
30–34 19 (22.6%)
35–39 27 (28.1%)
40–44 15 (12.6%)
45–49 30 (20.0%)
50–54 21 (15.7%)
55–59 19 (14.6%)
60–64 9 (10.3%)
65–69 10 (9.9%)
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 8 o 11
Pa icipan s a isk o discon inua ion could be iden i-
ied ea ly in he s udy while pa icipan s a isk o wi h-
d awal could no . We sugges ha di e en measu es
could be applied o he wo g oups. Fo example, an app
including ques ionnai es, push eminde s o ill hem in,
and elemen s o gami ica ion (applying game mechanics
o non-game con ex s in o de o keep pa icipan s en-
gaged [26]) migh p e en passi e discon inua ion, bu
no ac i e wi hd awal. Too in usi e eminde s could
e en s imula e wi hd awal. Depending on he eason o
wi hd awal, which we did no assess, eassu ance o da a
p o ec ion as well as he s udy’s impo ance o science
and socie y and egula eedback wi h s udy esul s
migh suppo con inuing pa icipa ion. The same is ue
o he discon inue s. Knowing in ad ance ha hose
who need mo e suppo in he beginning main ain his
a i ude c ea es he oppo uni y o add incen i es. How-
e e , hese hypo heses will ha e o be in es iga ed in u-
u e s udies. Fu he esea ch abou a i ion in heal h-
ela ed panels is needed, o example andomized con-
olled ials (RCT) ha examine he e ec o measu es
agains discon inua ion among pa icipan s who had o
Fig. 3 Kaplan-Meie cu es o discon inua ion (in he ex ended phase) by mode p e e ence
Table 5 Fac o s associa ed wi h pa icipa ion in he ex ended phase
Model C:
pape -and-pencil pa icipan s
(asked o swi ch o online mode)
Model D:
online pa icipan s
(asked o s ay in he s udy)
Be a Odds a io Be a Odds a io
Age a baseline (pe 10 yea s inc ease) no selec ed in his model 0.24 1.27
Ma i al s a us:
unma ied s. ma ied
no selec ed in his model 0.27 1.31
WHO-5 well-being index (pe 10 poin s inc ease) no selec ed in his model 0.01 1.01
PSS sco e (pe 1 poin inc ease) −0.02 0.98 −0.01 0.99
ID-Sc een (pe 1 poin inc ease) 0.01 1.01 0.04 1.05
Time be ween in i a ion and e u n o he illed
in o med consen o m (pe week)
no selec ed in his model 0.05 1.05
Numbe o ques ionnai es e u ned du ing ini ial phase
a
(pe ques ionnai e)
0.19 1.21 0.43 1.54
Numbe o imes a pa icipan had o ecei e
eminde emails du ing he ini ial phase (pe eminde )
no applicable o
pape -and-pencil pa icipan s
−0.27 0.76
Va iables we e selec ed using he leas absolu e sh inkage and selec ion ope a o me hod in logis ic eg ession
ID Sc een: mean sco e based on in ec ions and in ec ion-associa ed symp oms in he las 12 mon hs (sco e anges om 0 [no in ec ions in he las 12 mon hs] o
46 [mo e han 42 in ec ions in he las 12 mon hs])
PSS: pe cei ed s ess scale (sco e anges om 0 [ e y low s ess le el] o 16 [ e y high s ess le el])
a
Pape -and-pencil pa icipan s ecei ed a o al o wo ques ionnai es; online pa icipan s ecei ed a o al o ele en ques ionnai es
Rübsamen e al. BMC Medical Resea ch Me hodology (2017) 17:132 Page 9 o 11