His o y o labou ma ke a achmen
as a de e minan o heal h s a us:
a 12-yea ollow-up o he No he n
Swedish Coho
Anna-Ka in Waene lund,
1
Pe E Gus a sson,
1
Anne Hamma s öm,
1
Pekka Vi anen
2,3
To ci e: Waene lund A-K,
Gus a sson PE,
Hamma s öm A, e al.
His o y o labou ma ke
a achmen as a de e minan
o heal h s a us: a 12-yea
ollow-up o he No he n
Swedish Coho . BMJ Open
2014;4:e004053.
doi:10.1136/bmjopen-2013-
004053
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To iew hese iles please
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(h p://dx.doi.o g/10.1136/
bmjopen-2013-004053).
Recei ed 18 Sep embe 2013
Re ised 14 Janua y 2014
Accep ed 16 Janua y 2014
1
Depa men o Public Heal h
and Clinical Medicine, Family
Medicine, Umeå Uni e si y,
Umeå, Sweden
2
School o Heal h Sciences
and Ins i u e o Ad anced
Social Resea ch, Uni e si y o
Tampe e, Tampe e, Finland
3
Depa men o Public Heal h
and Clinical Medicine,
Epidemiology and Global
Heal h, Umeå Uni e si y,
Umeå, Sweden
Co espondence o
D Anna-Ka in Waene lund;
annaka in.wae[email p o ec ed]
ABSTRACT
Objec i e: The p esen s udy aims a using ajec o y
analysis o measu e labou ma ke a achmen (LMA)
o e 12 yea s and a examining whe he labou ma ke
acks ela e o pe cei ed heal h s a us.
Design: Da a we e e ie ed om a 26-yea
p ospec i e coho s udy, he No he n Swedish
Coho .
Se ing and pa icipan s: All nin h g ade s uden s
(n=1083) wi hin he municipali y o Luleå in no he n
Sweden we e included in he baseline in es iga ion in
1981. The as majo i y (94%) o he o iginal coho
pa icipa ed a he ou h ollow-up. In his s udy, 969
pa icipan s we e included.
Measu es: Pe cei ed heal h s a us (psychological
dis ess and non-op imal sel - a ed heal h) a age 42
and he da a ob ained om ques ionnai es.
Resul s: We ha e iden i ied ou acks in ela ion o
LMA ac oss he 12-yea pe iod: ‘pe manen ’,‘high
le el’,‘s eng hening’and ‘poo le el’o a achmen .
LMA his o y ela es o psychological dis ess. High
le el (OR 1.55 (95% CI 1.06 o 2.27)), s eng hening
(OR 1.95 (95% CI 1.29 o 2.93)) and poo a achmen
(OR 3.14 (95% CI 2.10 o 4.70) in ol e highe OR o
psychological dis ess compa ed wi h pe manen
a achmen . The o e all p alue emained signi ican in
he inal model (p=0.001). Analyses ega ding non-
op imal sel - a ed heal h displayed a simila pa e n bu
his was no signi ican in he inal model.
Conclusions: Ou esul s sugges ha heal h s a us in
mid-li e, pa icula ly psychological dis ess, is ela ed
o pa e ns o LMA his o y, o a la ge pa
independen ly o o he social isk ac o s and p e ious
heal h. Conside a ion o he e ogenei y and ime in LMA
migh be impo an when analysing associa ions wi h
pe cei ed heal h.
INTRODUCTION
Du ing he pas h ee decades o so,
demands o a mo e flexible wo k o ce ha e
inc eased all o e he wo ld. Flexibili y in he
labou ma ke is eflec ed, o example, in
he p opo ion o empo a y employees,
which in ecen yea s has a ied be ween
13% and 15% o he o al wo king popula-
ion in Eu ope.
1
To he indi idual, he conse-
quence o flexible employmen is ha
a achmen o a wo kplace is weak and com-
monly in e up ed by unemploymen and
o he episodes ou o wo k. In o de o
cap u e he o al spec um o employmen
ela ions, wi h ega d o quali y and quan i y,
we ha e chosen o wo k wi h he concep o
‘labou ma ke a achmen ’(LMA) in his
s udy. In ou defini ion o he LMA spec-
um, we ha e included pe manen , non-
pe manen employmen , unemploymen and
hose who a e exemp ed om wo king.
2–4
Some ela ions be ween labou ma ke
s a us and heal h s a us a e widely accep ed:
pe manen employmen is conside ed bene-
ficial o heal h, while unemploymen is
known o ha e ad e se heal h e ec s
5–7
and
being ou o he labou ma ke in he long
e m is commonly due o poo heal h.
8
Bu
when i comes o he heal h implica ions o
labou ma ke s a us, be ween he ex emes
o he LMA spec um, he e idence is much
sca ce . P e ious s udies ha e p oposed ha
empo a y employmen could be a isk o
poo psychosocial wo k cha ac e is ics,
9
wi h
empo a y employees mo e commonly
expe iencing job insecu i y and ha ing a low
S eng hs and limi a ions o his s udy
▪Using longi udinal da a wi h excep ionally high
esponse a e.
▪Applying ajec o y analysis which only has p e-
iously been spa sely used in his ield.
▪P o ides a uniquely ich and de ailed da a on
empo a y con ac s o e a long pe iod o ime.
▪Relies on sel - epo ed da a.
▪Used a ela i ely small sample.
Waene lund A-K, Gus a sson PE, Hamma s öm A, e al.BMJ Open 2014;4:e004053. doi:10.1136/bmjopen-2013-004053 1
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cash ma gin,
10
which a e some o he ac o s ha can be
po en ial pa hways linking weak LMA o poo heal h. We
ha e, o example, shown ha long- e m empo a y
employees o en expe ience di ficul ies wo king ull- ime
(unde employmen ) which influences hei financial
si ua ion in a nega i e way
11
and can hus be a sou ce o
wo y.
12
Poo heal h can also be media ed h ough job
s ain, al hough i seems as i his g oup is a ec ed mo e
by limi ed influence o con ol a he han high
demands.
13
Mode a e LMA has been highligh ed as
po en ially ha m ul o heal h s a us, bu esea ch on he
opic is di e gen .
14
While some s udies epo wo se
sel - a ed heal h among empo a y employees,
15
a ew
s udies e en sugges be e sel - a ed heal h among
fixed- e m employees.
16
Some s udies also indica e ha
de e io a ion in sel - a ed heal h may no be obse able
un il he a achmen is qui e weak.
17
A majo answe o
he mixed esea ch esul s may lie in he inhe en di fi-
cul y in cap u ing he changeable na u e o employ-
men . Measu emen o he employmen si ua ion a one
o a ew poin s in ime, as in mos o he p e ious
s udies,
18 19
may o e look he ac ual exposu es o di e -
en posi ions. Heal h e ec s o empo a y employmen
could su ace a e se e al yea s o accumula ion, as we
ha e shown in a p e ious epo ,
20
o e en when se e al
yea s ha e passed a e he exposu e.
21
Mo eo e , i is
possible ha i is he chain o passages in di e en
employmen s, he ajec o y o LMA, ha con ibu es o
heal h s a us; o example, becoming mo e s ongly
a ached o e ime could con ibu e o heal h s a us di -
e en ly han becoming less a ached o he labou
ma ke e en i he bo h g oups hold same o al
exposu e.
The e a e a lo o s udies abou pa icula labou
ma ke s a us as p edic o s o heal h. An inhe en
p oblem o such s udies is he amoun o exposu e:
c oss-sec ional in o ma ion abou s a us includes g ea
a ia ion, a a iable based on he du a ion o he
ongoing s a us is bound o use c oss-sec ional heal h
da a, and in p ospec i e ollow-up se ings he e may be
pe iods in se e al s a us du ing he ollow-up. The
p oblem is o special impo ance in esea ch on he
heal h e ec s o a ypical employmen , as he e a e a
wide ange o s a us be ween pe manen employmen
and o e unemploymen . To add ess his opic, we ha e
in oduced a sco e ha sums up he exposu e o di e -
en ypes o non-pe manen employmen du ing he
ollow-up.
20
The sco e, howe e , does no ake in o
accoun he iming o he exposu es. One way o cap u e
he s a us chains, o he passages in and he ansi ions
be ween di e en labou ma ke posi ions, is p o ided
by ajec o y analysis. Applying his me hod wi h a ou -
class esponse a iable (pe manen employmen , non-
pe manen employmen , unemploymen and ou o he
labou o ce), he membe s o he No he n Swedish
Coho ha e been clus e ed in o six di e en ‘LMA
acks’.
2
Fo he ajec o y analysis o he p esen s udy,
LMA was measu ed by a 10-class indica o , in o de o
a icula e in mo e de ail he ajec o ies o non-
pe manen employmen and hei associa ion wi h
heal h.
The ew a ailable s udies abou labou ma ke ajec-
o ies in he field o public heal h ha e measu ed LMA
a a ew ime poin s, o example, be ween one ime
poin and ano he
9
and he goal has been desc ip i e
a he han analy ic.
19 22
In he p esen s udy, we ha e
applied a efined scale wi h ega d o LMA. In he
measu e, we ha e included a spec um o a ious ypes
o employmen si ua ions and also co e ed a ime-span
o 12 yea s. The me hod, ajec o y analysis,
23
o e s a
no el way o iden i y di e en ial acks o LMA his o y in
ou popula ion coho . A e ob aining a ele an se o
acks, ou aim is o examine in which ways hey ela e o
non-op imal sel - a ed heal h o pe cei ed psychological
dis ess.
METHOD
Popula ion and p ocedu es
The s udy was ini ia ed in 1981 and included all pupils
in hei las yea o compulso y school (n=1083), in he
medium-sized indus ial own o Luleå in no he n
Sweden (95% o he coho we e bo n in 1965). Since
1981 ou addi ional ollow-ups ha e been conduc ed.
24
The a i ion a e in he mos ecen ollow-up om
2007 was low; 94% (n=1005) o he o iginal coho who
we e s ill ali e (n=1071) pa icipa ed. Comp ehensi e
ques ionnai es, comple ed by he pa icipan s in 1981,
1983, 1986, 1995 and 2007, we e used as he main assess-
men me hod. This pape is based on da a om he
1995 and 2007 ollow-ups. P ocedu es o da a collec ion
a e desc ibed mo e ex ensi ely elsewhe e.
24
The s udy
was app o ed by he Regional E hical Re iew Boa d in
Umeå, Sweden.
Measu emen s
LMA his o y
We name he esponse a iable o he ajec o y analysis
as LMA. I aims o se e as a concep ual and empi ical
ool o so he employmen s a us o he pos indus ial
labou ma ke along a con inuum.
25 26
C udely, i ‘ e e s
o whe he o no people ha e con inuous employmen
(eg, all yea o only pa o i ) and whe he o no hey
ha e pe iods o unemploymen ’
27
A headline le el
28
he e a e ou majo classes o LMA: non-employmen ,
unemploymen , empo a y employmen and pe manen
employmen . Wi hin each class, se e al subclasses can be
disce ned. In he p esen s udy, he in e es is ocused
on di e en ial empo a y employmen . Seen h ough
LMA, empo a y employmen co e s a se o posi ions
defined by o mal job con ac s, ega dless o he psy-
chological con ac ,
29
job commi men
30
o pe cei ed
job insecu i y.
31
Pa icipan s’labou ma ke posi ion om 1996 o 2007
was measu ed wi h a ma ix consis ing o columns ep e-
sen ing hal -yea pe iods and ows ep esen ing di e en
2Waene lund A-K, Gus a sson PE, Hamma s öm A, e al.BMJ Open 2014;4:e004053. doi:10.1136/bmjopen-2013-004053
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labou ma ke posi ions. Wi h he ins uc ion ‘Du ing
which pe iods ha e you been employed pe manen ly o
ha e had some ype o empo a y job con ac o ha e
been ou o wo k?’ he esponden s we e p omp ed o
choose among 11 esponse op ions o each 6-mon h
pe iod: ‘pe manen ly employed’(coded as 10), ‘en ep e-
neu ’(9), ‘employed in p ojec ’(8), ‘subs i u e’(7), ‘p o-
ba iona y employmen ’(6), ‘on-demand wo ke ’(5),
‘seasonal wo ke ’(4), ‘ empo a y employee o o he
easons’(3), ‘in employmen policy measu e’(2),
‘unemployed’(2) and ‘ou o he labou ma ke ’(1).
Unemploymen and pa icipa ion in policy measu e we e
me ged, and each op ion was coded o a a iable ha
exp essed he s eng h o LMA on a scale om 10 o
1. The anking o con ac s has been es ed in p e ious
esea ch on he accumula ion o empo a y employmen
20
and was based on A onsson’sco e–pe iphe y model,
32
which p oposes ha he e is a heal h g adien in ela ion
o he ype o employmen con ac . The model anks con-
ac s based on du a ion, possibili y o on- he-job aining,
au onomy and job secu i y.
32
Howe e , we ha e ex ended
he anking by also including h ee labou ma ke posi-
ions o non-employmen . In he e en o ‘ou o labou
ma ke ’, a con inuum o fi e o mo e pe iods (ie,
2.5 yea s) was equi ed: i he e we e ewe han fi e, all
pe iods we e coded acco ding o he las labou ma ke
posi ion, o pu posely exclude hose on pa en al lea e o
s udying om his ca ego y. As he las ca ego y, ‘ou o
labou ma ke ’was gi en he lowes sco e in ela ion o
LMA. The in en ion o his g oup was ha i was supposed
o be con ained by hose mainly on sickness benefi (sup-
po ed by analysis, da a no shown), no hose empo a ily
no wo king due o pa en al lea e o educa ion. These
ope a ions hus yielded a sco e o he s eng h o LMA o
each o he 24 successi e hal -yea pe iods. The sco es
se ed as he da a o he ajec o y analysis.
Indica o s o heal h s a us
Psychological dis ess a ages 30 and 42 was measu ed wi h a
ques ion ha inqui ed whe he he esponden had expe i-
enced in he p e ious yea any o he ollowing symp oms:
es lessness, concen a ion p oblems, being wo ied o
anxious, palpi a ions, anxie y o panic o o he ne ous p o-
blems. Repo ing one o mo e o he six symp oms was
coded as 1 and none as 0, equalling a dicho omisa ion in o
he qua ile wi h he mos symp oms e sus he es . The
ques ion was de i ed om he ‘Su ey o li ing condi ions’.
33
Non-op imal sel - a ed heal h a ages 30 and 42 was mea-
su ed wi h one ques ion, ‘How do you a e you gene al
heal h?’, wi h esponse op ions: good, a e age o bad.
33
The esponses we e dicho omised in o he qua ile wi h
he wo s heal h (a e age o bad) coded as 1, and he
es (good) coded as 0.
10 34
Co a ia es
Socioeconomic posi ion is a s ong p edic o o
heal h.
35–38
LMA has been shown o be ela ed o occu-
pa ional class.
39
I is impo an o conside
socioeconomic posi ion as a possible con ounde when
s udying he ela ionship be ween empo a y employ-
men and illness. In his s udy, socioeconomic posi ion
(SEP) in 2007 was based on one ques ion abou occupa-
ion, which was classified acco ding o he Swedish socio-
economic classifica ion o occupa ional ca ego ies.
40
Uppe whi e-colla and sel -employed we e coded as 0,
lowe whi e-colla wo ke s we e coded as 1 and blue-
colla wo ke s we e coded as 2.
Pa ne ship and pa en hood a e also impo an
ac o s in ela ion o LMA as hese wo may be pos -
poned due o insecu e wo king a angemen ,
39 41
which
could influence social aspec s ela ed o illness.
39
Ma iage o ha ing a pa ne is also impo an o con-
side when s udying LMA, as i can be beneficial o
heal h and financial esou ces.
42
Pa en al s a us in 2007
was coded as 0 o hose ha ing child en and as 1 o
he childless. Ma i al s a us in 2007 was measu ed wi h
one ques ion: ‘A e you ma ied o co-habi ing?’yes was
coded as 0 and no as 1.
Mo e women han men ha e poo LMA in e ms o
empo a y employmen .
43
Gende has been conside ed
as an impo an ac o in ela ion o poo LMA and
illness, whe e women’s heal h migh be a g ea e isk.
44
Women we e coded as 0 and men as 1.
S a is ics
The pa icipan s we e clus e ed acco ding o he de elop-
men o hei LMA o e he 12 yea s applying ajec o y
analysis.
23
The me hod has been es ablished as a way o
s udying indi idual de elopmen al cou ses o e age o
ime, and o iden i ying dis inc i e g oups o indi idual
ajec o ies wi hin he popula ion ha eme ge, ins ead o
p edefined c i e ia, om he da a i sel . T ajec o y analysis
consis s o h ee s eps. Fi s , he app op ia e p obabilis ic
model is chosen o he esponse a iable. The second
s ep is o define he deg ee o he polynomial o m o he
ajec o ies. Finally, he numbe o he clus e s is decided,
employing he s a is ical in o ma ion c i e ia and he
‘common sense c i e ia’wi h espec o he subs ance and
aims o he s udy. As a esul , he de elopmen al ajec o -
ies wi hin clus e s a e as simila as possible, and ajec o ies
be ween clus e s a e as di e en as possible.
45
A indi idual
le el, clus e membe ship is dic a ed by he highes calcu-
la ed pos e io p obabili y o belonging o a pa icula
clus e .
T ajec o y analyses we e conduc ed wi h he Mplus
p og am package. The analysis allowed o 12 ime
poin s, and he fi s and he second hal o e e y second
yea we e chosen in o de o ake in o accoun he pos-
sible sys ema ic seasonal a ia ion o LMA.
We used logis ic eg ession (OR and 95% CI) o es
whe he LMA his o y was associa ed wi h non-op imal
sel - a ed heal h and psychological dis ess a age 42.
Adjus men s we e made o he heal h indica o a age
30, gende , socioeconomic posi ion, pa en al s a us and
ma i al s a us. SPSS V.17 was used o he eg ession
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analyses. Women and men we e analysed oge he o
p ese e powe .
RESULTS
The da a consis o a 10-class o dinal indica o o LMA,
and he o m o p obabili y dis ibu ion o longi udinal
sequence o measu emen o such a iable is he mul i-
nomial dis ibu ion.
The adjus ed Bayesian in o ma ion c i e ion (BIC)
alue dec eased om 17435.474 o he linea model o
16656.622 o he quad a ic polynomial model, indica -
ing ha he la e can be p e e ed o he o me . O he
in o ma ion c i e ia p o ided by he Mplus p og am like-
wise poin ed in he same di ec ion.
The op imal numbe o ajec o ies was sea ched by
checking he solu ions up o 1. The Adj. BIC was used o
choosing he solu ion.
46
The Adj. BIC alue (as well as he
o he in o ma ion c i e ia) dec eased when he numbe
o ajec o ies was inc eased, apidly a he beginning and
slowe a he end. F om se en- ajec o y o eigh - ajec o y
solu ion, he figu e dec eased om 17856.940 o
17606.402. The ea e he dec ease slowed down. We
decided o con inue wi h eigh ajec o ies, as his solu ion
p o ided, in addi ion o de ailed depic ion o di e en ial
LMA, he oppo uni y o exclude he clus e wi h 0 LMA
ha was ou side ou esea ch in e es .
Figu e 1 illus a es he ‘labou ma ke acks’based on
means o he LMA sco es a each ime poin o he indi-
iduals classified in o each ajec o y. Indi iduals on
ack 1 (3% o he coho ) also we e excluded, as hey
we e mainly disabili y pension ecipien s and hei
heal h was poo by defini ion. The ack (6) o ‘pe man-
en ’employmen h oughou he ollow-up included
mo e han hal o he coho , whe eas he emaining six
clus e s we e ela i ely small and he e we e ela i ely
simila acks. We collapsed hese six clus e s in o h ee
as ollows. A conside able pa (classes 2 and 3) main-
ained a con inuously ‘high le el’o a achmen , and
abou 12% (classes 5 and 7) displayed a ‘s eng hening’
o a achmen owa ds he end o he ollow-up. The
a achmen was pe manen ly weak in abou 1 o 10
(class 8), and a small clus e wi h a U-shaped pa e n
(class 4) was also seen; we decided o collapse hese clus-
e s and defined hei a achmen as ‘poo ’. In addi ion
o being subs an ially g ounded, his collapsing p o ided
s a is ical powe o subsequen analyses. Thus, we
a i ed a a ou class ‘LMA his o y’ a iable ha com-
p ised ‘pe manen ’(class 6), ‘high le el’(classes 2 and
3), ‘s eng hening’(classes 5 and 7) and ‘poo ’(classes
4 and 8) LMA (figu e 2).
Table 1 shows he dis ibu ion o he key a iables by
LMA his o y. In gene al, LMA his o y wi h less s ong
a achmen en ailed poo e heal h a age 42.
Conce ning co a ia es, simila pa e ns we e seen o
psychological dis ess and non-op imal sel - a ed heal h
a age 30, hus indica ing ha heal h s a us di e ed
be ween LMA his o y al eady a baseline. The e we e
also significan di e ences wi h ega d o socioeconomic
posi ion; he p opo ion o blue-colla wo ke s was
highes in he g oup wi h poo a achmen o he labou
ma ke . The poo a achmen g oup was also mos likely
o be li ing wi hou a pa ne (p=0.010). Pa en al s a us
did no di e be ween he g oups. The p opo ion o
women was highe in s eng hening and poo -le el
a achmen , whe eas he pe manen and high-le el
a achmen we e domina ed by men (p=0.001).
To analyse whe he LMA his o y was ela ed o poo
heal h, sel - a ed heal h and psychological dis ess we e
eg essed on LMA his o y wi h pe manen a achmen as
he e e ence ca ego y, in mul iple logis ic eg ession
models ( able 2). The LMA his o y had a significan
o e all p alue on bo h heal h ou comes. In unadjus ed
analyses wi h psychological dis ess, lowe s eng h o
a achmen in ol ed highe odds han he pe manen
one ( able 2, model 0; LMA his o y p<0.001). In model
0, we ound inc eased OR in ela ion o lowe a ach-
men o he labou ma ke , anging om high le el OR
1.55 (95% CI 1.06 o 2.27), s eng hening OR 1.95 (95%
CI 1.29 o 2.93) and poo OR 3.14 (95% CI 2.10 o
4.70). Adjus ing o co a ia es (sociodemog aphic and
psychological dis ess a age 30, models 1 and 2, espec -
i ely) esul ed in a enua ion o he ORs o hose wi h
‘s eng hening’and ‘poo ’a achmen . Finally, in he
ully adjus ed models (model 3), only he high le el and
poo a achmen we e significan ly ela ed o psycho-
logical dis ess, wi h he ‘poo ly’a ached displaying he
nume ically s onges associa ion (OR=2.52 CI 1.59 o
3.98). Al hough bo de line significan , he OR o he
‘s eng hening’(OR=1.57 (95% CI 0.99 o 2.49)) a ach-
men was o compa able s eng h o he ‘high le el’
a achmen (OR=1.54 (95% CI 1.01 o 2.35)). While
wi h a sligh dec ease in OR along wi h adjus men s o
sociodemog aphic ac o s and p e ious heal h, he same
pa e n is s ill e iden in he final model, and he o e all
p alue emained highly significan (p=0.001).
Resul s o non-op imal sel - a ed heal h we e sligh ly
less p ominen han o psychological dis ess bu
poin ed in he same di ec ion. Unadjus ed models
( able 2, model 0) showed a significan o e all ela ion-
ship be ween LMA his o y and sel - a ed heal h
(p<0.001), and he LMA his o y wi h ‘s eng hening’
(OR=1.57 95% CI 1.05 o 2.36) and ‘poo ’(OR=2.26 CI
1.53 o 3.34) a achmen had highe odds o ha ing non-
op imal sel - a ed heal h. Fo hose wi h ‘high le el’
(OR=1.38 CI 0.96 o 2.00) o a achmen , he isk was
nume ically highe , al hough no significan ly, han o
hose wi h ‘pe manen ’a achmen . A e adjus men o
heal h s a us a age 30 (model 2), he esul s o he
‘s eng hening’g oup we e a enua ed below signifi-
cance. In he final model, only he OR o he ‘poo ’
a achmen g oup was significan ly high, while he
o e all p alue o he associa ion o LMA his o y wi h
non-op imal heal h d opped o bo de line significance
(p=0.087).
4Waene lund A-K, Gus a sson PE, Hamma s öm A, e al.BMJ Open 2014;4:e004053. doi:10.1136/bmjopen-2013-004053
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DISCUSSION
In his s udy, we ha e iden ified ou acks o LMA his o y
o e 12 yea s: pe manen , high le el, s eng hening and
poo . Compa ed wi h he coho wi h ‘pe manen ’a ach-
men , we ound a highe p obabili y o psychological dis-
ess among h ee coho s wi h non-pe manen LMA. The
di e ences we e pa ially a ibu ed o p e ious heal h and
o some ex en also o sociodemog aphic a iables; ne e -
heless, he o e all con ibu ion o LMA his o y emained
significan in he ully adjus ed model. The esul s o non-
op imal sel - a ed heal h we e simila bu somewha
weake .
Much o he p e ious esea ch has sugges ed ha em-
po a y employmen is a s epping s one owa ds mo e
s able employmen .
47
In he p esen s udy, we ound
ha , al hough he g ea e pa o he sample al eady
had a ai ly s ong a achmen o we e mo ing owa ds
s onge a achmen , one ack emained poo ly
a ached o he labou ma ke o e he 12 yea s. Thus,
while he s epping s one hypo hesis migh be co ec o
he majo i y, a subs an ial mino i y appea s o be
apped in an employmen si ua ion o pe manen em-
po a iness. Fu he , we ound mo e women han men in
his leas a ou able si ua ion. This is p obably explained
by he widesp ead use o ‘on-demand employmen con-
ac s’in women-domina ed sec o s o business
43
such as
ca e and wel a e and educa ion
48
which a e wo indus-
ies which oge he s and o 33% o all empo a y con-
ac s in Sweden.
11
These esul s can be in e p e ed as
showing ha , e en hough Sweden is conside ed one o
he op- anked gende -equal coun ies wi h ega d o
high labou ma ke pa icipa ion among women, he
in e nal labou ma ke is s ill gende -seg ega ed.
Ou findings impo an ly sugges ha , in addi ion o
he p esen LMA, he LMA his o y is impo an o
heal h. In line wi h p e ious esea ch, we ound ha he
g oup wi h leas a achmen had he wo s heal h
s a us.
15 17
As in ou p e ious epo showing a cumula-
i e e ec o empo a y employmen on heal h s a us,
20
he p esen epo u he co obo a es ha
Figu e 1 The numbe o coho
membe s clus e ed by ajec o y
analysis in o eigh acks (cu es
based on means o he
a achmen a he ime poin s).
Figu e 2 Collapsed acks o
labou ma ke a achmen his o y;
pe manen , high-le el,
s eng hening and poo
a achmen .
Waene lund A-K, Gus a sson PE, Hamma s öm A, e al.BMJ Open 2014;4:e004053. doi:10.1136/bmjopen-2013-004053 5
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employmen his o y impac s on heal h s a us. Howe e , a
mo e nuanced pic u e eme ged when he sepa a e
labou ma ke acks we e conside ed.
Fi s , e en hose wi h ‘high-le el’a achmen expe i-
enced psychological dis ess mo e commonly han hose
wi h ‘pe manen ’a achmen . Thus, i appea s ha e en
ma ginal exposu e o wha could be labelled ‘LMA
s ess’can con ibu e o psychological dis ess o e ime.
Second, he g oup wi h ‘s eng hening’a achmen
s ill expe ienced poo heal h mo e commonly han
hose wi h pe manen a achmen , e en a e adjus -
men s o sociodemog aphic a iables. This esul sug-
ges s ha ea lie subop imal a achmen has a
po en ially ‘sca ing’e ec . I is impo an o poin ou
ha in c oss-sec ional o sho - e m longi udinal designs,
he ‘s eng hening’g oup would ha e been ega ded as
ha ing a ai ly a ou able LMA. This pa icula finding,
he e o e, s esses he impo ance o aking he specific
pa e ns o he long- e m labou ma ke his o y in o
accoun when examining associa ions wi h heal h s a us.
Thi d, among hose poo ly a ached o he labou
ma ke is whe e we ound he highes ORs o poo
heal h. The poo ly a ached wo ke s we e also mo e
likely o ha e o he isk ac o s o psychological dis ess,
which seemed o pa ly accoun o he associa ion. Fo
example, being single in ol es a lowe a e age house-
hold income and dec eases he le el o con ol,
49
and
poo p e ious heal h could also con ibu e o di ficul ies
in ge ing a s able a achmen o he labou ma ke , as
hose wi h heal h oubles could be less employable, pa -
icula ly o blue-colla occupa ions.
50
The poo ly
a ached wo ke s a e also hose wi h mos expe ience o
unemploymen , which p e iously has been connec ed o
mo ali y and mo bidi y.
551
Thus, he poo men al
heal h in his g oup seems o be a esul no only o
hei endu ingly un a ou able LMA his o y, bu also o a
ange o coexis ing bu densome li e ci cums ances. As
desc ibed in he in oduc ion, job insecu i y, financial
s ess, lack o ecip oci y, unce ain y and lack o au on-
omy a e some o he b oad ange o po en ial pa hways
linking empo a y employmen o poo heal h in p e i-
ous s udies.
9101552–54
Al hough media ing mechanisms
has no been wi hin he scope o his a icle, ou esul s
can be unde s ood in he ligh o po en ial pa hways p e-
sen ed in p e ious esea ch.
Me hodological conside a ions
Ou s udy elies on ajec o y analysis, a me hod ha
became a ailable in he beginning o he 2000s, la gely
by i ue o inc eased compu ing powe . Ins ead o p e-
fixing al e na i e de elopmen s, he analysis is seeking
de elopmen al ajec o ies ha eme ge om he da a
i sel .
17
I gi es each indi idual pos e io p obabili y
alues o each ajec o y, and alloca es hem acco ding
o he highes p obabili y in o g oups o ca ego ies so
ha indi iduals wi hin a g oup a e mo e simila han
indi iduals be ween g oups.
55
To ou knowledge, ajec-
o y analysis has been used only spa sely in p e ious
s udies abou LMA.
56
Ou p e ious esea ch using a
co e–pe iphe y s uc u e has only yielded a measu e
summa ising he o al accumula ion o pe iphe al
employmen o e 12 yea s,
20
whe eas his s udy has
added new knowledge o he field by showing when
exposu e akes place and has p o ided pa e ns o
labou ma ke his o y, and his specific knowledge has
hin ed abou po en ial sca ing e ec s o poo LMA
(seen in he s eng hening g oup), knowledge ha has
p e iously been hidden due o me hodological limi a-
ions. In gene al, his s udy ep esen s no el me hodo-
logical ideas in a esea ch a ea ha has been obscu ed
Table 1 Dis ibu ion (%) o dependen and independen a iables in ela ion o labou ma ke a achmen (LMA) his o y
Pe manen ,
n=550
High le el,
n=163
S eng hening,
n=126
Poo ,
n=130 p Value
(χ
2
es )T ack 0 1 2 3
Dependen a iables a age 42
Psychological dis ess 26.3 35.7 41.0 52.8 <0.001
Non-op imal sel - a ed
heal h
29.1 36.2 39.2 48.1 <0.001
Independen a iables
Heal h s a us a age 30
Psychological dis ess 19.4 27.3 36.3 31.9 <0.001
Non-op imal sel - a ed
heal h
16.8 29.4 26.6 33.3 <0.001
Sociodemog aphics <0.001
Blue-colla wo ke 33.5 25.8 35.7 47.7
Lowe whi e-colla wo ke 15.7 8.0 18.3 6.2
Uppe whi e-colla wo ke 50.8 66.3 46.0 46.2
Single ma i al s a us 19.1 20.9 22.2 32.6 0.010
No child as pa en al s a us 17.3 16.6 15.1 19.4 0.831
Women 44.5 42.3 61.9 55.4 0.001
All alues a e displayed in pe cen , excep p alues.
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by he p ac ice o measu ing he labou ma ke posi ion
c oss-sec ionally o wi h sho - e m ansi ions be ween
labou ma ke posi ions.
The longi udinal design o his s udy has been an
asse , as i made i possible o adjus o p e ious heal h,
and he eby educed he possibili y o e e se causa ion,
and especially as he a i ion a e was kep low.
Conce ning he gene alisabili y o his s udy, his coho
has been shown by a p e ious assessmen o be ep esen-
a i e o Sweden as a whole wi h espec o demog aphic
da a.
24
I is plausible ha heal h e ec s o poo LMA
ope a e depending on he social con ex . Fo example,
heal h implica ions migh be mo e o less e iden
depending on s uc u al ac o s such as na ional labou
ma ke policies, educa ion sys em and legisla ion.
57
Sweden is pa o he Scandina ian wel a e egimes
which a e conside ed o ha e s ong Social Democ a ic
alues and go e nmen - unded benefi s du ing episodes
o unemploymen . The wel a e s a e Sweden could,
he e o e, possibly educe nega i e heal h e ec s o flex-
ible employmen ,
58
which is in con as o he esul s in
ou s udy. Howe e , Swedish unions ha e c i icised he
cu en labou ma ke egula ions o being oo libe al
ega ding empo a y employmen . Wi h cu en egula-
ions, i is possible o hi e a subs i u e o up o 2 yea s
and a e ha hi e he same pe son on a gene al em-
po a y employmen con ac o up o 2 yea s. This
causes a si ua ion whe e people a e a isk o becoming
long- e m empo a y.
59
As a esul o his, app oxima ely
10% o all empo a y employees ha e been employed by
he same employe o 5 yea s o mo e. The Swedish
labou ma ke egula ion could, he e o e, be a eason
o he no iceable finding in his s udy, whe e a subs an-
ial pa o he wo ke s ollowed emained poo ly
a ached o e he 12 yea s which we e examined.
Long- e m empo a y employmen could be a u u e
p oblem, and also a ele an g oup o s udy u he in
u u e esea ch.
The sample size was limi ed in his s udy, which is a
poin e o po en ial u u e esea ch, which would
benefi om analysing da ase s wi h a la ge sample size.
Such s udies would be able o s a i y analyses o gende
o socioeconomic posi ion, which could en ich he
unde s anding o he field o LMA and illness. In his
s udy, we ha e ocused on poo LMA as a isk ac o o
poo heal h, bu he e a e a ange o o he ci cum-
s ances ela ing o p eca ious employmen which could
explain he esul s, such as ulne abili y, lack o benefi s,
low wages and disempowe men .
44
The e o e, we would
ecommend u u e esea ch o elabo a e on o he
aspec s o p eca iousness linked o poo LMA, as well as
explo ing he alidi y o he phenomena in a di e en
con ex , o example, coun ies wi h di e en social and
labou policies.
This s udy is based on sel - epo ed da a. Equi alen
measu es o sel - a ed heal h and psychological dis ess
ha e displayed good alidi y by p edic ing u u e mo al-
i y and mo bidi y
60
e en a e adjus men s o known
heal h isks.
61
Fu he mo e, using e ospec i e measu e-
men o LMA his o y could lead o ecall bias.
Ne e heless, e ospec i e ques ions abou occupa ional
his o y ha e been shown o main ain good quali y in
e ms o ag eemen wi h census da a.
62
Fu he , he ac ha we combined acks could be seen
as a limi a ion o his s udy. Howe e , in ou unde s and-
ing, some o he acks could be combined depending on
hei simila mo emen in he labou ma ke . We fi s
analysed each o he eigh acks sepa a ely in ela ion o
he ou come, o make su e ha none o he combina ions
esul ed in blu ing o he esul s (da a no shown). One
limi a ion ega ding he me hod was ha , due o ea u es
o he p og amme, only hal o he ime poin s (12 o 24
possible ime poin s) could be included in he ajec o y
analysis. Howe e , we used he fi s and second hal o
e e y second yea o educe he possibili y o sys ema ic
e o due o seasonal a ia ions in employmen s a us.
Table 2 Logis ic eg ession analyses o wo ou comes a age 42 in ela ion o exposu e o LMA his o y (OR (CI 95%))
T ajec o ies Model 0 Model 1 Model 2 Model 3
Psychological dis ess as ou come
Pe manen , n=550 1 1 1 1
High le el, n=163 1.55 (1.06 o 2.27) 1.56 (1.06 o 2.30) 1.50 (0.99 o 2.28) 1.54 (1.01 o 2.35)
S eng hening, n=126 1.95 (1.29 o 2.93) 1.77 (1.17 o 2.69) 1.68 (1.07 o 2.66) 1.57 (0.99 o 2.49)
Poo , n=130 3.14 (2.10 o 4.70) 2.77 (1.83 o 4.19) 2.87 (1.83 o 4.49) 2.52 (1.59 o 3.98)
p Value o LMA <0.001 <0.001 <0.001 0.001
Non-op imal sel - a ed heal h as ou come
Pe manen , n=550 1 1 1 1
High le el, n=163 1.38 (0.96 o 2.00) 1.46 (1.00 o 2.13) 1.19 (0.81 o 1.76) 1.26 (0.85 o 1.87)
S eng hening, n=126 1.57 (1.05 o 2.36) 1.52 (1.00 o 2.29) 1.44 (0.94 o 2.20) 1.40 (0.91 o 2.16)
Poo , n=130 2.26 (1.53 o 3.34) 2.00 (1.34 o 3.00) 1.83 (1.21 o 2.77) 1.65 (1.08 o 2.53)
p Value o LMA <0.001 0.003 0.025 0.087
Model 0 c ude ORs.
Model 1 ORs adjus ed o sociodemog aphic a iables (socioeconomic posi ion, gende , ma i al s a us and pa en al s a us).
Model 2 ORs adjus ed o heal h s a us a age 30.
Model 3 ORs adjus ed o models 1+2.
Waene lund A-K, Gus a sson PE, Hamma s öm A, e al.BMJ Open 2014;4:e004053. doi:10.1136/bmjopen-2013-004053 7
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The s uc u e behind he concep ualisa ion o LMA
needs conside a ion. The LMA s uc u e is based on he
idea ha he e is a g adien in he labou ma ke , wi h
some posi ions being mo e s ongly a ached o he
labou ma ke han o he s. We ha e used a modified
e sion o A onsson’s co e pe iphe y model
32
o o de
he ype o employmen con ac /si ua ion, om he
mos a ached o he leas a ached o labou ma ke .
Ou s uc u e is, indeed, a simplifica ion o a mo e
complex eali y; his should be conside ed when in e -
p e ing he esul s. The LMA a iable and socio-
economic posi ion a e pa ly o e lapping, as he g oup
o en ep eneu s is pa o he SEP classifica ion and he
LMA a iable. This o e lap could cause o e -adjus men
in he logis ic eg ession analysis. As hese wo a iables
pa ly measu e he same phenomenon, adjus ing o
socioeconomic posi ion could adjus o pa o he ue
e ec o LMA.
CONCLUSIONS
Policymake s equen ly p omo e flexible employmen
con ac s. Howe e , his s udy shows ha hose wi h he
mos a ou able bu long- e m high-le el a achmen
su e om wo se heal h han hose pe manen ly
a ached. Fu he , despi e a de elopmen owa ds a ou -
able employmen ci cums ances, heal h disc epancies
can endu e, sugges ing a po en ially ‘sca ing’e ec .
Finally, hose poo ly a ached display he wo s heal h
si ua ion, which is pa ly due o coexis ing bu densome
li e ci cums ances. We fi mly sugges ha policymake s
should conside he esul s o his s udy and ake espon-
sibili y o c ea ing employmen oppo uni ies sui able
o main aining a heal hy wo king li e, a he han p o-
mo ing employmen con ac s cha ac e ised by poo
a achmen o he labou ma ke .
Acknowledgemen s The au ho s would like o hank all he pa icipan s in he
No he n Swedish Coho . Liudmila Lipiäinen and Tapio Nummi a e hanked
o con ibu ing o his pape wi h ega d o he ajec o y analysis. The
au ho s also hank Alan C ozie o p o essional language edi ing.
Collabo a o s Liudmila Lipiainen; Tapio Nummi.
Con ibu o s AH, PEG, PV and A-KW ha e subs an ially con ibu ed o
concep ion and design. A-KW and PEG ha e con ibu ed o analysis and
in e p e a ion o da a. A-KW, AH, PV and PEG ha e d a ed he a icle and
e ised i c i ically o impo an in ellec ual con en . All au ho s ha e gi en
hei inal app o al o he e sion o be published.
Funding This wo k was suppo ed by Swedish Council o Wo king Li e and
Social Resea ch [2006-0950] he Medical Facul y a Umeå Uni e si y and he
Academy o Finland [g an numbe 132668 o PV]. The s udy has been
inanced by The Swedish Resea ch Council o En i onmen , Ag icul u al
Sciences and Spa ial Planning dn 259-2012-37.
Compe ing in e es s None.
E hics app o al Regional E hical Re iew boa d in Umeå, Sweden.
P o enance and pee e iew No commissioned; ex e nally pee e iewed.
Da a sha ing s a emen The No he n Swedish Coho is no eely a ailable.
Resea che s who in e es ed in collabo a ion should ge in o con ac wi h he
P incipal In es iga o , Anne Hamma s öm; anne.hamma s [email p o ec ed]
Open Access This is an Open Access a icle dis ibu ed in acco dance wi h
he C ea i e Commons A ibu ion Non Comme cial (CC BY-NC 3.0) license,
which pe mi s o he s o dis ibu e, emix, adap , build upon his wo k non-
comme cially, and license hei de i a i e wo ks on di e en e ms, p o ided
he o iginal wo k is p ope ly ci ed and he use is non-comme cial. See: h p://
c ea i ecommons.o g/licenses/by-nc/3.0/
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