occupational injuries and illnesses : new evidence from the

I 5 8 8 Th e i m p a c t f ve r t i m e a n d l n g w r k h u rs n ccupatinal injuries and illnesses : new evidence frm the U n i te d S ta te s A E Dem be, J B E rl cksn, R G De l bs, S M Banks Occup Envirn Med 2005;62 :588-597. dg O. 1 1 36/em, 2004. 0 1 6667 S ee e nd f a r t i c le fr a u th rs' a fi l ia t i n s C rre sfnden ce I : As c i a le Pr Fe s sr A Dembe Center fr H ea l th F' ic'.t & Resea rch, U n ive r s i ty f Ma s sa c h u s e tt s Med ical S chl, 22 2 Ma e Ave nue, H igg n s gu i d lng, Shrewsburyt MA 01 545, USA; Al la rd. Dembeg uma s smed.edu Accepted 8 March 2005 Ai m s : T a na lyse lhe impact f ve rti me a nd exlen ded wrki ng hu rs n the r i sk f c cupa ll nal in ju r es and illnesses amng a natinally representdib'e sample f wrking aduhs frm the United Stdies. Melhds : Re sp n s e s fr m 1 0 793 Am e r i ca n s pa r l lc ipa t i ng i n the Na l i na l Lng l tudi na l Su rvey f Yu lh ( N LSY ) we re u s ed l eva l ua te w rke?s ' ]b h i s t r ies, w rk s ch edu le s, a nd cc u r re nce f ccu pa ti na l i n ju ry a nd i llne ss be een 1 987 a nd 2000. A I ta t 1 1 0 236 j b recrds were ana D'sed, e ncmpassing 89 729 persn-years f accumufted wrking time. Ag rngaled incidence rates in each F five expsure categries were calculaled fr each NLSY survey perid. Mullivadate ana tical techniques were used l estimdie lhe relalive risk f lng wrking hurs per day, exleeded hurs per week, lng cmmute times, a n d ve rtim e sch ed u l es n rep rting a w rk rela led i n ju ry r i l l n ess, a fter a dj us li ng fr age, gen de r, ccu :gi n, i ndu s lry, a nd regin. Results : After adjusting fr thse fdrs, wrking in jbs with vertime schedules was assclaled with a 6 1 % h i ghe r i n j ury haza rd ra te cmpa red t j bs wi thu t vertim e. W rking a l ba s t 1 2 hu rs per day was as sc i a ted wi th a 37% i n creased ha za rd ra te a nd wrki ng a t lea s 1 60 hu rs per wee k wa s as sc lalnd with a 23% increased hazard rate. A slrng dse-respanse efecl was bserved, wilh lhe injury rale (per 1 00 accumulaled wrker-years in a particular schedule ) increasing in crrespndence t Ihe number f hurs per day (r per week) in lhe wrkers' cuslmary schedub. Cnduslns: Results snggesl Ihl jb schedules with lng wrkifig hurs are nt mre risky merely because lhey are cncentraled in inherently hazardus induslhes r ccupatins, r because peple wrking lng hurs spend mre lfl time "at risk" fr a wrk injury. Sfrdiegles t prevent wrk injudes shuld cnsider cha nges i n schedu l i ng p ra c l l ces, jab redesig n, a nd h ea fih p r tectin p rg ra m mes f r pep le w r k i ng i n jbs invlving vertime and exlended hurs. g r wing b dy f evidence s u g ges t s that ln g wrk ing hurs a dve r s e ly a f fect th e heal th an d wel lb e ing f wrke r s. S tu d ie s h ave a s scia ted vertime a nd extended wrk schedules with an increased risk f hyperten s in, ca rdiva scula r d i s ea s e, -9 fa t igue, O- l s t re s s 4-7 d ep re s s in/ mu s cu l s ke le tal d i s rder s/ ' - ' chrnic infec t in s, d i abete s/' general hea l t h cmpl a in t s/ -2 and a ll cause mrtality3 S everal revi ews a nd met a - a n al ys e s h a ve b een published summ a r i sing the s e re s earch fin d in g s? " Sys tema t ic reviews g enera l ly h ave cn c luded th a t ln g wrk in g h u r s a re p te n t i a ny dangeru s t w rkers ' he a l th. Hwe ver, exi s t ing re s earch i s spars e a n d incnsi s t e n t ha m a ny a rea s. Cmpa ra t ively few s tu d ie s have e amined t he impa c t f lng wrk h u r s n w rkers' ri s k f r ccupatinal inj u rie s and ill n e s se s. S m e s tu d ie s h ave detec ted evi dence f a re] a rian be tween ln g wrki ng hu r s a n d an in crea s e d ri sk f ccup a t inal i nj uri e s amng w rke r s in specifi c ccupa t in s a nd indu s trie s, incl ud i n g cn s truc tin wrkers, nu rse s, 4 a na es the ti s t s, ' veterin ari ans, ' t her h ea l t llca re prfe s s ina l s/3 "a m iner s," b u s d rive r s,* ' l ng d i s ta nce t ru ck d rivers) " fi re -figh ter s / a nd nucl ear pwer p lant w rker s. In ne f the nly studies invlving the manufacturing sectr, an i n crea s e d ri s k f s evere h and injuries wa s fun d fr Hang Kng fac tary wr ker s w rking m re t han 1 1. 5 hurs per d ayy A large s cale cr s s - indu s try s tudy f 1. 2 millin G e rm an w rke r s ' cn pen s a t i n re c rd s fu nd th a t th e ri sks f n n - fa ta l an d fa ta l w rkplace acc id en t s increa s e during th e la t ter p r t in ( a fter the: e ighth hur ) f a lng wrk s hift / 2 Simil a r fn dings f an increa s ed ri sk f wrk injurie s du ring t he la t te r p r t in f ln g s hi f t s h a s a l s b een b s e rved in s t udie s frm S candinavi a an d the Uni ted Kin gdm." " O ther re sea rchers h ave inve s t igated t i re a ffe c t f succe s s ive lng s hi ft s and t he length f re s t b rea k s b e tween sh i ft s a s p s s ible ri s k d e termin an t s f r indu s t r ial a c c id e n t s? Neve r th e le s s, re s e a rchers' und e r s t anding f th e hnpa c t f lng wrkin g hurs n wrkp l ace inj u r ie s r em a i n s i ncm ple te a nd eqdivc a l. Several inves t iga tin s h ave fun d n evide nce f an a s s ci a tin, ' * r h ave b served a prtec tive effec t. ' ' Authri tie s h ave nted th at m any ex i s t in g s tudie s h ave s er i u s methdlgical s hr tcmin g s, includin g sm a l l s amp le s i ze s, u nique indus try s pecific circums t ances th a t l im i t genera g s abig ty f the Findings, and t he fa i lu re ta accunt fr p tent ial cn funding fa c t rs. Fr example, j b s perf rme d during lng wrking shi fts m i gh t be inh e rently mre d a nger us, r pepl e wrking in ex tend e d - hur s chedu le s nfigh t h ave d i ffe ren t pers na l ch a rac te r i s t ic s ( f r ex ample, age, ge n de r, r und er lying heal th s tatu s ) tha t a ffec t their injury risk. Additinally, the vast majrity f existing s tu d ie s have b een pe rfrm e d in Eu rpe, A s ia, an d S ca nd i n avi a. Only a h and ful f s tud i e s h ave b een cnducted in the United States, and nne f them have bwalved large sample s ize s r s!udy ppu l atin s repre sen ti ng a mix f ind u s t r i e s a nd ccupa t i n s. Thi s a r t i c le repr t s n a s tudy f th e imp ac t f veri im e and ex tend ed w rk ing h u r s n t he ri sk f ccup a t ina l i njuri e s and i l lne s se s amn g a na t in a l ly repre sen ta t ive s ample f wrking adul t s frm t he United S ta te s. The s tudy span s 1 3 yea r s and d raw s n infnnarin cntain ed in 1 1 0 2 3 6 j b recrd s, Mult iva r i a te a nalys e s are emp lyed t WW ', C,((:eNv ed,corn

Ove r l lm e a n d fa n g w r k h u rs 5 8 9 Dem a ndi n g w r k s c h ed u le Ove I fi me tng w k hu rs F igure 1 C nc e tua I m de 1 F the re a t n s h T be twe e n dem ndi n w rk s ched u 1 e s nd c upa i na i n [u r ies a nd i nesses (ed p t ed r m : h u s e r a nd Shde s 2 ). cn t r l fr the in flue nce f wrke r s ' age and sender, regin, in du s t ry s ectr, and ccupatin. The s tudy i s b a sed n the hyp the s i s tha t wrki ng ver t im e r an ex te nd ed wrk schedule ificreases the likelihd f reprting an ccupatinal injury r illness cmpared t wrkers having less demanding s chedule s. Mrev e r, we hyp fl l e s i se ti l a t the r i sk f injury in crea s e s witl i ncrea s ing vlume f wrk perfrme d in th e d eman din g s ched u le. The cnce p tu a l b a s i s f r thi s s t u dy i s ad ap ted frm a there tica l md e l prps e d by Michel S h us t er a nd S u s a n Rhde s i n 1 98 5 32 In till s m del, ver time and ln g h ur s f wrk are p re s ume d t a ffe c t the ri s k f wrkplace acc idents by p recipi ta t i ng va r ius int e rme d i a ry cn d i t i n s In a ffec t e d wrke rs, su ch a s fa tigue, s tre s s, a nd d rws i ne s s. The pa thway l in king a d e m and i n g w rk schedu le t t i le in term ed iary cndi t in a n d u l t ima tely t a wrkp lace a c c iden t ca n be med i a te d by a va r iety f indivi du a l and env i rnmen tm fa c t r s, including pe r s n a l ch a ra c teris t ics ( f r example, age, gende r, health s ta tu s, j b experience ), j b factrs ( fr example, inten s i ty f wr k, exps u re t h azard s ), and rgani s a t i nal factrs ( fr ex amp le, v e r t ime pl i cy, super vi s i n ) ( s ee fig 1 ). O u r s tudy an a lys e s the a s scia t i n b e twee n exp s u re t ver time a nd ex te nded wrk s ch edul e s a nd the incid e nce f rep r ted wrk rel a t e d i nju r i e s an d illne s se s, adj u s ting fr the influence f s everal medi a tin g fa c trs, i ncluding a ge, gender, ccupa t i n, indu s t ry s ec t r, a nd gegraphica l re g in. The specific mech a n i sms by which fatigue, stress, r ther intermediary cnditins bring abut a w rkp l ace a cc id ent a re n t inve s t iga te d in thi s reprt. M E I H O D S D a t a fr thi s s tudy cme s frm the Na t i na l ngitudi n a l S u rvey f Yu t h ( N LSY ), which i s spns red by tile US Bureau f Labr Statistics and adnainistered by the Ohi State Un ive r s i ty Cent e r fr Hunl a n Re surce Res earch. The NLSY chr t i s cmpri s ed f 1 2 68 6 men a nd wmen wh were 1 4 2 2 year s f age wh en fi r s t su rveyed in 1 979. Fl l w up in telviews wi th N LSY re spnd e n t s h a ve been cnd ucte d annua lly frm 1 9 79 t 1 9 94, and biannual ly s ince 1 996. B ecau s e f NLSY funding re s tra in ts, n que s tins cnce rning wrk rel ated inciden t s were included in the 1 9 9 1 s urve y and ti xere f re thi s yea r f da t a wa s exclu ded, Th e NL SY cllec t s in f rm a t i n n re spndent s ' s ci d emgraphic chara c teri s t ic s, h u s ehld cmp sitin, educa t in, tra in in g, d e t a i led w rk h i s tri e s, jb a n d emplyer charac teri s t ic s, incme and as s e t s, hea lth insurance s tatus, hi c i de n ce f wrk rel a ted i nj urie s a nd i l lne s s e s, epi sde s f wrk d is ab ility, and re spndents' s cial and dme s t ic func t ining. Th e s u rvey' s s ampl ing s t ra tegy wa s de s i gned t b e re p r e s en t a t ive f the nndn s t i tu tinafl s ed civi li an s e g m e n t f yung pepl e l iving in the Uni ted S ta te s in 1 97 9 and b na b e twe en 1 January 1 9 5 7 a n d 3 1 D ecember 1 964. Additinally, NLSY ve r - s ampled c ivi l ian Hi spa n ic, b lack, a nd ecnmically di s advanta ged white yuth t h elp d e tec t variatins in emplyment and health cnditins accrding t re spnde n t s ' race, e thni city, a nd s c iecn mic s tatu s. S ubj ec t s fr ti le survey we re selec ted ba s ed n the res u l t s f 5 7 000 hu sehl d s creeni ng in t erview s cnduc te d by ifie Na tin a l Opinin Re s ea rch Cen ter ( NORC ) a t t he Un iver sity f C lfi eag. ' N LS p rvide s s ampl in g we igh t s fr e a ch re spn se t reflec t ti e n a ti n a l d i s t r ibuti n f Ame r i ca n s in this a ge ran ge. Thi s s tudy examined ti l e experience f t he s e individuals be t sveen 1 98 7 a nd 2 000. A t tempt s we re ma de t re -in t e rview eve ry rema in ing chr t m embe r a t each s u rve y. Surve y re spn s e rate s fr th s e yea rs ( excl ud in g d ecea s ed re spn den ts ) ranged frm 9 1. 0% fr the 1 98 8 sur ve y t a hi gh f 92.5% In 1 989 a n d a l w f 83.4% in 2 000. During th a t pe rid, 1 0 7 9 3 member s f tile chr t reprte d wrking in at lea s t ne j b. Amng emplye d chr t memb er s, 5 2.2% were male, 1 3. 2 % were bla ck, and 6.7% were f H i sp anic e thniclty (we ighted percen ta ge s ). A j b recrd wa s created fr each p s i t in held by a n ind ivi d ua l d uri ng each survey pe rid, wi th a "j b" d efine d as a chrt m emb e r b e ing emplyed in a par t icul a r p s i t in f r a spe c ifi c emplyer wi th a p s i t in s tart d a te and ( i f a p plicab le ) en d da te prvided. If an individu a l held mre than ne p sitin a t a time ( fr examp le, fr d i ffe re n t empl ye r s ), an ther jb recrd wa s cre a te d t re flect the in d ivi dual ' s experience s in the psitin s held cnc urren t ly. C hange s Hectr in g wi thin a p s i t in { f r example, changes in j b a ctivities ) did n t re sul t in the creatin f a new jb his try recrd, bu t a new recrd wa s crea ted when a wrker ch ange d p s i t in s ( f r example, a m achhd s t b ecming a s upervi sr ). A t ta l f 1 1 0 2 3 6 jb r ecrd s $'ze re avai l ab le f r analy s i s, encmp a s s ing a t tal f 89 729 persn-years f accumulated wrking time. Each jb recrd c n ta ined ex tensive s elf-rep r ted infm atin abut th e charac teri s t i c s f the j b in c lud ing the d a te f b e g inning wrk in th e j b, the end date ( if applicable ), j b re spn s i b il i t ie s and ac tivi t ie s, ccupa t in a l ca te gry, emplye r' s industry sectr, jb lcatin, custmary wrk schedule, usual d a ily j b s ta r t ing and end ing t ime s, cmmuting t ime, and WW V,OCCHI tvmd, tl

5 9 O D e m b e, E r i c k s n, Oe l b s, e t a l Ta b e 1 C l racte r i s t i c s F the w rkers reprl ng w rk re la ted in ju r i e s a nd i l l nesse s, we ighted da ta i u r e s _ Wrk rda tc Hn ju-s _ - end gtn prted nd ne ce$ jbs wlth Chamcte stks d rite w er ng a - n a g s - an expsure* - w ated Jn 'Ju y fnes 5139 n=2799 Mb (%} Age n n yers B & ce I%1 Ft i spnk e thn clb. (,%} Fm b, ;nch e [ rren d ar l Scbfing, cmpbled (meaa yeats) Reg in N he s Nrlh Cen tra l Wes t Ur b n esk? e c J O:u lbn da i afn ( 1 Pr, sinl nd ted nkl Sa. Oe w cc kers :a l Machi ne p era. s Lbu e s. ex cep l frm 6 1. I 3 1.7 1 1.2 6.8 $334 1 9 12.6 1 6.6 3 1.0 3 1.8 20.6 27.4 " 1 1.0 9.3 1 5. 1 1.7 67.7 2 :i 1 1. 2 7.0 9 35502 1 2.6 1 6.9 3 1 6 32.4 9, t 29. 5 9.7 0. 5 2,5 9.4 1 7. 6 22. 6 9.0 1 6. 5 2.2 infrmatin abut vertime wrk and the receipt f vertime pay. Fr the p urp s e s f thi s s tudy, five exp s ure ca tegrie s were speci fi e d : Extended hu rs per week : Jb s in which t he re spnde n t rep r te d re gu l a r ly w rk ing 6 0 r mre hur s p e r w eek we re c n s i d e red t have this exp s ure. Ex t ended hurs p er day : Jb s in which the re spnd en t reprted regularly wrking 1 2 r mre h u rs per d ay were cn s idere d t h a ve thi s exp sure. Overt im e : Fr the 1 98 8-9 3 surv ey yea r s, the indivi du a l ' s jb wa s cn s i d e re d t have this exp sure if the wrker re spn de d "ye s" t the que s tin: " Di d y u wrk verfime at tiris jb?". The NLSY survey did nt define the mealdng f "vertime" ; interpretatin f that term was left up t the d i scterin f the re spnde nt. Owin g t ch a n ges in the N L SY que s tinn a ire, frm the 1 9 94 t 2 000 s urvey years, th e i nd ividu a l' s j b wa s cnsi d e re d t h ave thi s exp s u re i f th e w rke r re spnded " ye s" t the que s t in : " ' At th i s j b, d i d yu u sually re ceive ve r t im e pay?". Ex tended card,mu te t im e : Jbs in which the re spn d ent rep r ted re gularly cmmu t in g tw r mre h ur s per d ay t and frm t he wrkpl ace w e re cn s idered t h ave thi s expsure. O vert im e r extended hurs : Thi s wa s a derived summary exp s ure vari ab le. A w rke r ' s j b wa s cn s idered t have thi s exp sure i f i t cntained any f the p re ced ing fur exp s t. lre s, Tire exp s u re ca te grie s we re n t mu t ually exc lu s ive a nd s a p a r ticul a r j b p ten ti a fiy cul d have ne r mre exp sure s. The primary u tcme f i n tere s t in t hi s s tudy wa s the self rep r ted incidence f a wrk re l a ted inj u r y r i llnes s. Th i s wa s ba s ed n a re spnde ngs a ffi rm a t iv e re s pn se t the flln vir g questin : " l wuld like t ask yu a few questins abut any iniuries r i l lnes se s yu m igh t have rece ived r gtte n wh i le yu were wrking n a jb. Since [dle f lasl intendew ] have yu had an incident el any jb lhat resulted in an injury r i l ln e s s t y u? " D uring the 1 3 year s tudy perid, 5 1 3 9 wrk rela te d i nj urie s and il lne s se s were reprted. O f th s e, 2 7 9 9 ccurre d in j b s having ex p s u re t a t lea s t ne f the f u r exps ure ca tegrie s. Tab le 1 summaris e s cha racteris t i c s f t he e f fec ted wrke r s and their firj ude s. F r the purp s e s f thi s a na ly s is, we a s s ume d t h a t the repr ted inju ri e s were in d epen d ent

I! Ove r i im e a n d l n g w r k h u r s 5 9 1 Table 2 J6b recrd wiih te rled w k telied i6 [ UdOs r llnesses lha t were induded ln lhe reg re s s i n 6 n6 i s cb m red io ih& e ih a t we?e exd ded, we lg h ied d la frm ne anther. Als, we assumed that a distinct wrker m a y suffe r m re th a n ne laj u ry, a nd in th a t ci rcum s tance, the wrker' s chara c teri s ti c s ( i n t able I and t he subsequ en t analyse s ) wuld b e cu n ted mre than nce. The s e pre sump Un s refl ec t typ i ca l pat tern s f acu te inj u ry c curre n ce and acc i dent re p r t ing in indu s t ria l s e t t ing s. Fr ex ample, i t w u l d nt b e u ncmm n f r a p a r t i cular w rker t fa l a n d spra i n an ankle n ne c ca s in an d th e n sub s equently ( pe rh ap s eve n in the s ame year ) sufer a d i ffe rent injury ( f r examp le, a cu t fin ger ) wi thut fl tere bein g a speci fi c cau s a l cnnec t in be twee n the tw events. Cru de ( u nadj u s ted ) ccu pa t inal inj ury and illne s s e s incidence rate s f r each f th e five exp s ure ca te grie s ( f r ea ch s urvey perid ) we re ca l c u la ted by d ividi ng th e t ta l ntmdier f wrk related injuries and illnesses reprted in jbs h a vi ng e a ch type f exp s u re by t he t t a l acc um u l a te d per sn - t ime w rked in t h s e j b s. The crud e inci de n ce ra te s fr each expsure categry were pltted graphically fr every NL SY surve y year frm 1 988 t 2 000 t de p i c t t rends ver t ime a n d t v i s u a lly pr t ray the rela t ive d iffe re nce in ra te s b etwe e n j b s wi t h a nd wi th u t each type f exp s ure ( tha t is, the rel a tive ra te ra ti ), hfrm a tin a but cnmm ti ng t ime wa s nly cllec ted i n NLSY s urvey years 1 98 8, t 9 93, and 1 994, a n d th u s trend lin e s fr th a t exp s ure ca tegry were nt g raphed. Ra te ra t i s, re flec t ing the re la t ive r i s k f rep r t i ng th e ccu rre nce f a n ccupa t in a l injury r i l lne s s, we re calcula ted by d ividi ng the incidence ra te f r t he a ccumu l a ted pe r sn- t ime in j b s wi th an exps u re by the inc i d ence rate fr a cc umu l a te d persn - time i n j bs wi th u t tha t expsu re. S, fr exampl e, in a par t icu lar s urvey perid, if 3 00 i nj urie s we re rep r ted t h ave c cu rred in j bs cntai n in g a t tal f 3 00 0 p e r s n- year s wi t h an exp s u re a nd 2 0 0 inj u r ies were rep r ted t h ave ccu rred in jb s cnta i nin g a tta l f 4000 persn - years withut that expsure, then the crude rate rati wuld b e 2. 0, ca lcul ated a s fl lws : ( 3 g inj urie sd O00 expsed persn-year s ) ( 200 inj urie s/ 40 00 tmexp s e d per s n-year s ) = 1 O.0 inj uri e s per 1 0 0 expsed prs n-yea rs + 5. 0 inj uries per l g unexps e d pers n- years = ra te ra ti f 2.0 TO adj u s t f r th e influ ence f s el ected cvari a tes, m u l t i variate analyses were prfnned t calculate hazard ratis fr each exps u re ca te gry u s ing Cx p rp r t in a l h a za rd s regre s s in techn iqu e s, which are u sed t analys e the e ffe c t f mu l t iple r i sk fac tr s ver t he t ime p re ceding t he ccur rence f an even t. The muh iva r ia te analy se s in c lude d a l l accumul a te d pe r s n - ting e f exp sure preced in g the fir s t injury in a particular jb during a sutvey perid, disregarding subsequent injuries and assciated expsure time in that jb during the p e rid. O f the t tal numb e r f w rk re lated :i nj urie s reprt ed ( 53 1 3 ), nl y 1 74 ( 3. 3% ) we re the s ecnd r s ub s eque n t inj ury in a l b during a s u rvey pe r id and thu s we re excluded frm the analys e s, O t her j b recrd s were exclud ed becau s e f ins u fficie n t infnn atin ab u t tire spe c i fic da te f i njury r t ime spen t n a jb, re s u l t ing in the exclu s in f a n a ddi t inal 3 70 i njurie s, a nd the ab s ence in sm e rec rds f s ample we ight s, re sulti n g in the exclu s i n f an a dd i t in a l fur i nj u r ie s ( a nd the a s s c i a ted exp su re thne ). We pe r fnned a c mpa r i sn f th e l b recrd s wi t h injurie s u s ed in the regre ssin an alys is ( 4765 ) t th e 3 74 recrds with missing data t deternfine if thse included and excluded were signi fica n tly diffe rent. The 1 74 " sub s equ en t i nj ury" rec rd s we re n t included in th i s cmp ari s n becau se by de fi ni tin they ha d the s ame j b ch arac teri s tics a s t h se i n c luded in th e 4765 jb rec rd s w i th fir s t inj u r i e s. O u r cmpari sn shwed th a t the recrd s exclude d frm the a n alys i s were very s im i l ar t th s e inclu d ed ( table 2 ). As a r e s u l t f the s e me thdlgica l cn s ide ra t ins, t h e re wa s a t tal f 1 0 9 08 7 jb recrd s and 4765 injurie s u s ed in the Cx p rp r t ina l regre s s in a n a lys e s f h a za rd ra t i s cmpared t 1 1 0 2 3 6 j b recrd s a nd 5 5 1 3 injurie s u sed in the c rud e an a lys e s f incidence ra te s a nd ra te ra t i s. S amp le we ights we re applied t d e r ive n a t i na l ly re p resen tat ive e s t im a te s fr indiv i d u a l s i n the NL SY age ra n ge ( 1 4-22 yea r s ld as f t 979 ; 2 2-43 years l d d uri n g the s tu dy perid frm 1 98 7 t 2 000 ). E ach re gre s s in m del inc lu ded the a ccumula ted per s n t ime fr ne f t i le five exp s ure ca te grie s a s the primary in depen dent va r i able, the rep r t ing f a wrk re l a ted inj ury r i l l ne s s a s the d e pendent va riable, and a ge ( cntinuu s va riabl e ), gend er (M!F ), re gin (Nr thea s t, S ut h, Nr th Centra l, We s t ), ccupa t inal g ruping (high ri s k /lw r i sk), a n d ind u st ry g rup ing ( high ri s k/l w ri sk ) included a s cvari a te s. "High ri s k" ccupa t in s in c luded U S Cen s u s ( I 970 ) Occu pa tin Cl a s s ifica tin C de s 40 1-5 7 5, 60 1-7 1 5, and 740-785 ( cra ft sm e n, fremen, pera t ive s, an d lab ure r s ), a nd " h ig h r i s k" i n du s trie s i n clu d ed U S Cen s u s ( 1 970 ) Indu s tri a l C l a s sifica ti n C de s 067-97 7 and 1 07-3 98 ( cn s tru c t in a n d m anu facturi ng sec trs ). * s T h e ccupa t in an d indu s t ry cd e s s e l e c te d fr inclu s in in the "hig h ri sk" ca tegrie s have traditin aly h igher than average ccupa t in a l inj u ry an d i l lne s s in c id en ce rate s a s repr ted by the US Bureau f Lab r S ta ti s tics. ** We te s ted the prprtina l h a zard s a s s ump t in and i t he ld f r e ve ry va riab le u sed i n the regre s sin md el with th e sle excep tin f regin. Hwever, WMt4t.OCC e t Wm. O ffl

! I 5 9 2 D e m b e, E ti c ks n, O e l b s, e t a l Ta b le 3 Types f in i u r le s a nd i l l nesses rep rted by w rke rs i n ib s w i lh a nd wi thu l exp su re, pe rce n l d l s l r i bu fin, we ighted da ta _ and illr sses n _ I, iudes and i n sses in bs 'm'th e x;p su re jb s wl tl-,u t e xp su re Type f iniu y c fness n = 2799 n = 2339- h'b se, s ele t l cnd tt,.n s 34.9.34. 4 Frad',s 7.8 7.4 Cut s a nd b se s 25.0 24.9 Bums 3.3 3.3 t he r frumatlc i n jure s 1 ;/. 2 1 1.6 Peripl i ne,. us systurt d sese 2. 8 2.7 Ot he r ccup tlna l d i se s s 9. 2. 1 0.2 Mi :dl neu s 4. 8 5.5 i n u r a nalys i s, re g in wa s cn s id e red nly a s a p ten t i a l cn fu n der. We d id n t d raw r rep r t any cn c lu s ins in thi s s tudy a b u t th e e llec t f re g in n the prpe n s i ty f r i nj u ry. Thu s, b a s ed n t fi*e gen e ral appli cabil i ty f the a s sump tin f r a l l f the prima ry exp sure variables and the ma in u tcom e s va ri a ble ( inj ury ) u s e d i n the an alyse s, we applied t l]e Cx p rprti na l app rach a nd repr ted the re s u l t s acc rd ing ly. C rud e inci dence rate s a n d ra te ra t i s we re c a l cula ted wi th SA S ( ver s in 8.0 ) s ta ti s t ica l sften,a re. 6 ' Th e PrQue s t s ft wa re sy s tem wa s u s ed t crea te a d a tab a se f j b s and pers n - t ime exp su re rec rd s,'* an d Cx p rp r t in a l regre s s in an a ly se s we re pe rf rmd n tha t d a taba se u s in g S ta ta S E ( ver s i n 7 ) s ta t i s t ical sftware. *' B e c au s e th e ha zard ra t i calcu la t in s we re ba sed n a sample ra the r than the NL SY s e ntire targe t universe ( An e rica n s a ge d 1 4-2 2 a s f 1 9 79 ), the re s u l t s were s ubj e c t t s antpl i ng e rrr. T accun t fr s ampfi ng e ffec t, 95 % cnfid ence interva l s a rund the h aza rd ra t i s we re e s t im a te d by a pply ing Ta y lr apprxima t in tecpmique s u s in g SUDAAN ( versin 7. 5 ) a n alytica l s ftware. ' R E S U L T S Table 3 summ a r i s e s the type s f injuries and ilhre s s e s repr t e d, amng p eple wrkin g in jb s with a nd wi thnt exp s u re. M s t rep r te d wrk rel a t ed cn d i t ins we re e i ther mu s culskele ta l d i s rd e r s ( 3 4. 7% f a l l rep r ted i nju ries ) r cuts anti b rui s e s ( 2 5. 0% ). T fie un a dj u s ted i ncidence rate fr til e ent ire du ra tin f th e s tudy wa s 7. 5 0 repr ted firj urie s p e r 1 00 w rke r -yea r s f r pepl e in j b s w i th exp sure t extended h urs pe r week, 2 9% h igher th a n t h e rate amng th se in j b s w i thu t exp sure t ex te nded hurs per week ( 5. 8 1 repr te d injurie s per 1 00 wrke r -yea r s ). Simi larl y til s e in j bs wi th exp s ure t ex ten de d h urs pe r d ay had an incidence rate 3 8 % h igher th an th s e in j b s withut that expsure ( 7. 97 v 5. 7 7 inj uri e s per 1 00 wrker -ye ars ), th s e in j bs with expsure t ve r t ime had an inddence ra te 84% h igher t h an th s e in jb s wi thut th a t exp sure ( 7.49 v 4. 0 6 inj u ri e s per 1 0 0 wrker -yea rs ), and ths e in j b s wi th exp s ure t ex tend e d cmmu te time h ad an inci den ce ra te 7% l wer th an th s e i n j b s wi thu t t ha t exp s ure ( 6. 90 v 7.4 6 inj urie s per 1 00 w rke r -yea r s ). Incide nce ra te s f r ea ch type f exp su re varied by surv e y year, w i th a gene ral d x'cnward t rend in inj u ry ra te s bs e ed frm 1 98 8 t 2 000 lb r a l l exp s ed a nd nn - exp sed g rup s ( fig 2 ). B e tween 1 988 a nd 2 000, ra te s amng the varius exp s ure ca tegrie s decrea s ed by 5 69 %. There were s m e fluc tu a t in s b s e rved in the re l a t ive gap between exp s ed and unexp s e d gru p s durin g the s tu dy peri d, b ut n ntab le t rend s in the relative d i ffe re n ce b e tween grups ver t ime we re d e tec ted. Th ere wa s a s tr n g p s i t ive rel a t in b s e rv ed b etw e e n the nr a gnitud e f expsure fr extended hurs per week and ex tend ed h u r s pe r d ay and the c r respnd i ng injury incidence ra te ( fig 3 ). Fr ex tended hurs per d ay, every a dd i tin a l five hur s per we ek ver 40 wa s a s scia ted wi th a n ave ra ge increa se f apprxlula t e ly 0. 7 inj uri e s per 1 00 wrke r - imurs. Fr ex ten d e d h urs p e r d ay, e ve ry a dd i t i nal 2 hurs per day ver 8 wa s a s sci a ted wi th an ave ra ge increa s e f apprx i m a tely 1.2 injurie s per t O0 wrke r - hur s. Table 4 s umm ari s es the unadj us te d rate rati s a n d 95% cnfidence in terva l s fr ea ch expsure cate gry an d the u n a dju s ted ha za rd ra t i s calcu l a ted u s ing fi r s t inj u rie s nly t hrugh th e Cx prprtinal meth d. The ra t i s a nd cnfid e nce i n tervals ca lcu l a te d by e ach me th d were genera l ly qu i te s imilar. The final a dj u s ted ha zard ra t i s c a lcula ted by the Cx p rp r t inal me th d s, after a dju s t ing f r age, gen de r, ccupa t in, in du s try, an d reg in, a re p re s e n ted in tabl e 5. The resu l t s f th e a djus ted analy s i s indica te s th a t til e a ss cia tin betwe en exps ure and the ri sk f i nj u ry wa s nly s l igh t ly a ffec ted by the in fl uence f t he se cvari a te s. Th i s analysi s fu nd th a t, a fter a dju s t ing f r t hs e fa c t r s, jb s w i th ex te n ded h ur s pe r day i lave a 3 7 % h igher injury haz a rd ra t e cmp a red t j b s wi thut th a t exp sure. S imil a r ly, w rkin g in a j b wi th e x t ende d hur s pe r week wa s a s s ci a ted with a 2 3 % ttigh er inj ury h a zard ra te, wrking in a jb wi til vertime wa s a ss cia ted wi t h a 6 1 % hi g her injury hazard rate, and wrking in a jb with airy vertime r exten d ed hur s s chedule a s a s s c i a te d vi th a 3 8% h i gher inj ury haza rd ra te. N a s s c i a t in wa s de te c ted be twe en wrking in a j b wit h ex tend ed cmm ute time and the inj ury h azard ra te. D I S C U S S I O N This s t u dy f n a t i nally repre s en t a tive d a ta frm til e Uni te d S ta tes ad d s t t he g rvin g b dy f evidence ind i cat ing t ha t wrk s ch edu les invlving l ng h urs r ver tim e s ub s tan t i ally increa s e s the ri sk fr ccupa tin a l injurie s and inj u rie s. Unlike previu s s t udie s, ur im,e stiga tin ha d the advan ta ge f cve r i ng a la rg e var iety f i b s, a n d cn t rll in g f r t i le pten t i a l cnfund i ng a ffect f age, gender, c cupa t in, industry, and regin. We analysed nearly 1 00 000 jb recrds ex tend i ng ver a 1 3 year perid, and emplyed s everal s t a t i s tica l t e chniqu e s fr qu a n t i fying the ex ten t f ri s k. "fhe re sul t s f thi s s tudy su g ge s t th a t jb s svi th lng wrkin g hurs a re n t mre r i s ky mere ly b ecau s e they a re cnce n t ra ted in inhere n t ly h azardu s indus trie s r ccupa t in s, r b ecau s e f th e d emgraphic charac teri s t ics f emplyee s w rking th s e schedule s. O u r finding s a re cns i s tent vi th the hyp the s i s tha t lng wrking hur s indirec t ly p re c ipi ta te wrkp lace acc id en t s thru gh a cau s a l p rce s s, fr in s tance, by in d ucing fa t i gue r s t re s s in a ffec ted w rke r s. Hweve r, u r find in g s a re a l s cns i s t ent svi th ther hyp the s e s and thu s we cannt be certain f a caus al cnnec tin b a s ed n this s tudy a lne. v,cw. cc:e nym ed. cm

Ove r t i m e a n d l n g w r k h u rs 5 93 Ex le nd ed h u rs pe r day 1 6.0 1 6,0 g -.- Exp Un e xp sed sed I g 1 `1 0 ;, 2. 1 0, 0 1 0. 0 8.0-8.0 & & 6.0 6.0 u 4, 0 `1.0 '= 2. 0 e 2.0 _. _' 0.0 1 9 8 8 1 98 9 1 990 1 992 1 993 1 994 1 996 1 99 8 2000 N LSY s u rvey yea r Ex t e n ded h u r s pe r w ee k -,.4.--- Exp sed [ Unexp s ed 1 9 8 8 9 8 9 1 990 1 992 1 993 1 99`1 1 996 1 99 8 2000 N LSY s u rvay ye a r & ] 2, 0 1 0. 0 B,O 6. 0,t.0 = 2.0, Ove rt i m e 1 2.0 -*- Exp sed " 1 0.0 U n exp sed 8.0 6.0 4.0 8 g 2.0 I I I! I I L I. 1 9 8 8 1 989 1 990 1 992 1 993 1 994 1 996 1 998 2 000 N LSY su rvey yea r Any vertime r exlended hurs J Exp sed I I I I I I t I! I 1 9 8 8 1 989 1 990 1 992 1 998 1 994 1 996 1 99 8 2 000 N LSY s u rvey yea r Figure 2 Trends ln incidence ra es f reprted w rk re ted n uries aed nesses n j bs w th and with u expsure by expsure categ. NLSY s urvey perids 988, } 989t 1 990, 1 992, 1 993, i 994, 1 996, 1 998, a nd 2000. Nle: N LSY ch anged the ", rd ing fr the questin regard ing vertime in 1 994, th e reby p ten t ially a fec t in g th e t rend l i nes f r "vert im e" and "any ve rti me r ext ended h u rs". O u r cmpar i s n f inj u 13 incidence ra te s f r w rker s in jbs with a nd wi thu t exps ure wa s nnna l i s ed by u sing a cmmn denmin a tr f l g wrker - y ears, thu s av i d ing a ctnmn me t hdlgi cal flaw tha t ha s a ffl icte d sme pre vi us s t u dies in th is field. Fr example, wrke rs wh, n a ve ra ge, w rk ln ger hurs ( f r example, 2 5 00 hu r s pe r yea r ) ca n be expe c ted t exp e rience mre injurie s than th s e wh w rk shr te r h u r s ( f r ex ampi e, 2 000 hur s per year ), even if the underlying r i s k s t b t li g rup s a re ac tua lly the s ame, b eca u s e th e f rm e r grup spend s mre t ime "at r i sk" f r i nj u ry. M a ny s tu d i e s th a t h ave b s erved mre i nj u ri e s am ng pers n s wh wrk lnge r hur s have fa i led t take I 0. 0 9.0 a 8. 0 _ 7.0 6.0 5.0 4, 0 8 3.0-8 " 2.0 1. 0 1 0, 0 9.0 8,0 7. 0 6. 0 5, 0. 4.0 8 3. "C, 2. 0 1. 0 O. 0 I I 1 I I I I 0,0 I I I < 4 0 `1 0-45- 50-55- 60-65 < 8 8-9. 9 1 0-1 1. 9 1 2-1 3. 9 M+ 44. 9 4 9. 9 5 4. 9 5 9. 9 6 4. 9 H u r s/w e e k H u r s/day Figure 3 Treeds in inciden e raies F reprted w rk re!ated in uries and i nesses n bs w h and w th ut ex su e fr tw expsure aieg ries ( hurs/week and hurs per day), by amunt f expsure. NLSY aggregated data cvering 1 987-2000. ", '.c cenwn ed, cm

5 9A Dem b e, E r l c ks n, D e l b s, e t a l Table 4 Unad u s led ra le ra f s ha za rd ra t is, a nd 95% c nfide nc e inte rva l s f r in j u r ie s r i l fn e s s e s rep r led in jbs wi l h exs ure t vertim e and extended hu r h edu es -. U ndj le Ur, lju sk,d Imza rd _ - Expsure ca tegri, " 95% Ct F 'cnded hurs/w k 1 60 ) 1.29 1. 18 t 1.42 1.29 1. 1 5 t k46 Exte,ded h 's/d (b l 2 ) I 38 1.26 t1.5 J 1. 46 1, 30 t 1. 63 Over x. 84 1.75 f 1.94 1. 84 t.70 i 2.00 Extended mna li me 2 t x s ] 0.93 0. 75 t I. ] 4 0.94 0.72 1 1. 22 Any b pe w- tlrne r exteexld hurs 1.41 1 25 1. 48 1. d8 1. 3 8 t 1. 59 N [SY da)a. t 98 7-2000. n = 1 1 0 236 ib recrds 0 rate ratis, 1 09 087 0 hazed r. d i s cn s id e ra t in in t accu n t ( a s wu ld happen, fr ins ta nce, i f incid e nce rate s were t b e calcula ted n the ba s i s f number f injurie s pe r 1 00 ftdl - time wrker s ). Thi s s tu dy cn tr l s f r tha t e ffec t by deri'img ra te ratis ( and h a z a rd ra t is ) wh i ch cmpare t he prpen s ity t s uffer i nj urie s in ea ch g rup d u ri ng a s ta nd ard l s e d perid f "a t ri s k" t ime. A n t abl e result f ur a n alys i s wa s t he de tec tin f a clear d se -re spn se effe c t, in wlfich the number f h u rs wrked per week ( ver 40 ) a n d the numb e r f hu r s wrked pe r d ay ( ver 8 ) were p s i t ively a s s ci ated wi th an increas ing risk f inju ry ( per 1 00 wrker -ye a r s ). Thi s finding lend s s upprt 1 the idea that there may be a causal prcess linking lng wrk schedule s wi t i l c cu p a t in a l inju ry. In thi s re spe c t, u r s t udy is cnsistent whh thersn- 2 t 7 that have shwn increasingly greater level f injury risk in the lat ter prtins ( fr example, b eyn d 9 h u r s ) f lng w rk sh i ft s. T sm e exten t, the decl in e in incid en ce ra te s b e twe en 1 98 8 and 2 000 b serve d in ur s tudy refl ect s the ge nera l dec l i ne in c c upa t in a l inj ury a n d i l lne s s rates r ep r t e d na tin aly duri n g th a! perid. Data frm t he 'U S B ureau f Lab r S tat is tic s ( B L S ) ind icate t ha t ccupa tina l injury and i l l n e s s ra te s ( a l l ca se, p r iva te ind u s try ) decrea s ed by 2 9 % during that prid, frm an average f 8,6 t 6. 1 reprtable cas e s pe r 1 00 w rker s? = Tha t decline h a s b een a t t r i bu ted t va rius p s sib le cau s e s, in clu ding s a fer wrkplace s and a s lfi ft frm ma nu fa c t u r i ng t service r i en ted j b s, which typ ica lly h ave lwe r average inci den ce ra te s." Anther fac tr th a t m ay help t expl a in th e re la t ively la rg e r ( 5 4-69% ) ra te decrea s e s b serve d in ur s t udy i s the a gin g f ur ch r t, wh were 2 3-3 1 years l d in t 98 8 and 3 5 43 yea rs ld a s f 2 00 0. Y unger wrke r s g en e ra l ly h ave h igher incid e n ce ra te s t h an lde r ne s, i n pa r t b ecau s e w rke r s tend t mve in t lwe r r i sk ccupatin s ( f r example, m ana geri a l and a d nl n i s t ra t ive ) a s th e y age. Our s tudy fun d t h a t ver tim e s ch e d ul e s had tl e grea te s t incrementa l r i s k f inj ury, wi th ver t ime w rker s havin g a 6 1 % hi gher inj ury haza rd ra te cmp ared t wrkers in j b s vi thu t ve r t ime, after cntrll ing f r age, gender, ccu pa t in, ind u s t ry, and reg in. Th i s finding i s cn s i s t en t wi th the r s t udie s tha t have identifie d vert hne wrk a s particu l a r ly h a z a rdu s? 2, 7. B u t fe w p r eviu s s tu d ies have cmp a red th e rela t ive ri s k f "ve r t ime" s che dule s t the r s che d u l e s wi th l ng w r ld ng hurs pe r day r p e r week. Indeed, t he mea ning f "vertime" i s n t p re d s e, and thu s the term might be used differently in different cntexts and lca t in s. Prir t 1 994, n specific defini tin f " vertime" wa s p rvid ed t NL SY respn den t s, a nd s the term culd have b een in terpre ted in a va rie ty f ways : referri ng, fr example, t lng wrk hur s, wrk t h a t exceeds th e re spn dent' s cnve n t ina l wrk sche d ule, unu sua l r un ex pec t e d hurs f wrk, r wrk th a t quali fie s t he w rker tb r ve r t ime pay. TO h e lp cl a r i fy thi s i s s ue, the w rd ing f t ile "ver t ime" ques t in i n N LSY wa s changed i n 1 9 94 t re fe r spe c ifica l ly t w rk t h a t qu a l ifi e s f r ver t ime pay. Und er the U S Fai r Lab r S t and a rd s Ac t f 1 93 8 ( P L SA ), emplyee s cve red u nder the a c t a re enti t led t rece ive ve r t ime p ay equ a l l ing a t lea s t 1 5 0% f the i r regul a r pay ra te fr a l l wrk t ime exceed i n g 40 hur s pe r week. I t wa s e s t im a ted tha t t he FL SA cve r e d 74 m i l lin Am e rican wrke r s i n 2000, ab ut 7 9 % f the US civi l ian l abu r f rce?s 6 On avera ge, app rx im a te ly 2 0% f cvered w rke r s rece ive ver tim e pay i n any week? 7 During the 1 9 9 0s, the ave ra ge wee k ly ve r t ime hurs put i n by man ufa c turing wr kers cve r e d by PL S A g rew b y 2 5 %., W r ke rs exemp t frm FL SA cverage includ e m s t a dmini s tra t ive, p rfe s s i nal, execu t ive, s upen, i sry, and u t s ide s a le s pe r s nnel wh a re pai d n a s al aried ba si s. New regul atin s recently p rmulga ted by the U S Depar tme n t f Labr h ave ex tended the FLSA exemptins t an additinal 8 millin white - cllar w rkers. 9 In th e U SA, apprx imately 1 9-3 3% f vertime wrk i s mandatry ( als called "cmptdsry", " frced", r "invlun tary,, ) 7s, Mandatry vertime is vertime wrk required by em p l ye r s, fte n under the threa t f j b ls s r th e r pen a l ty i f t he w rker fa i l s t cmply. Seve ra l s tud i e s h ave s ugge s ted t h a t m a n d a try ver time is e s pecially haza rd u s wi t h re s pect t i t s a f fe c t n wrker fa t igue, s tre s s, impaire d p e rfrm a nce, and the ptential fr accidents, especially in the nursing and healthc a re p rfe s s in s 2 5 The NLSY d id n t d i fferentiate b e tween m a n da try and vlun tary ve r time, and i t i s n t currently ad dre s s ed r re g u la ted by the F L SA. Our study als fund greater injury risks assciated with wrk sche dul e s exceedin g 60 hu rs per week and 1 2 h urs per d ay. The s e specific va lues fr ide n t i fying " ex tend ed hur s" we re ch s en ba sed n p reviu s re s earc l x s tudie s whi ch h ad d e tec ted i ucrea sed r i s ks a t th s e level s. ' * ' 2 3., ra te S rep rted i n b s l h e p su t:e t vert i c[ ex i nd hu r sched u les, a fter n tr l l ihg f r ag e; g nder, ccu i ii$; i ndu s (d/, 6nd reg in : p r e ca tegw ba rs/day (! 2 1 1 3 ;r 1 1 6 ] 59 ; Over,m4 1 :6 t 1 :43 1 1 79 i WWW, c<ceflv ed, COIT t

[ Ove r t im e a n d l n g w r k h u rs 5 9 5 i i]2 L ',( L ' d v ' a 'm ve d ime, rk r ex ien de h ea se s lh ri s Ove li e sch edu les h a d th rete s t-m Ta 'dve r! s k f cc u pa lln a! ju ry!" q l ln e ss, ffw d by s c edu le w l t l ex ten d d ex ten d Th e-rlsk- i u r, wa [und I i e 6se wi th = ih e -e S t ra l l es f r _ pmvenlihg w lac e n j u de s and 1 [ ncrea s l ng I fg th l e w6 sc hed ]e ves f - :-n ss e s shuld c de - ch cmg es n rk."gg 0!! c n trl fin r- enti re amdnt F w r i t ime s n t a nd b d gn ad m ss'mg lh e [e, glh ' rk sch ed les.... a t r s k m t u ry : -- _ -, a nd qhe e rf rma ce F e rl n rn. - : Hwever, increa sed r i sk s a l s h ave b e en de tec te d a t ther wrk - t lur leve l s by a va riet y f re s earchers and t here i s a s ye t n cns e n s u s cri t e rin f r the p reci s e am tm t f wrk th a t is c n s ide red t b e ha z ardu s. In an at tempt t crea te unifrm lab ur s t a nd a rd s, the E u rpea n Unin i s s ued a Wrking Time Di rec tive in 1 9 93 th at limi ted nrm al wrkh g h u rs t n mre tha n 48 pe r w eek ( avera g ed ver a fu r mn t h pe rid ) and s p e c i fie d ther requ i remen t s rel a te d t rest breaks, shift wrk, and vertime. Sme Eurpean natins ( tb r example, t h e OK) h ave i n trduced prvi s in s fr wrkers t vlun ta ri ly p t ut f th e s e requ i rements r t therwi se p rvide fl ex ibil i ty in the i r im p lemen tatin. S tu d y l i m i t a t i n s Thi s s t u dy wa s ba s ed n sel f- repr ted Iffrm a tin frm NL SY chr t memb e r s regard i ng t hei r emplyment and inj ury/il ln e s s e s expe rie nces. Re spnde n t s were a sked t reca l l infrm a t in frm fi le t im e f the p reviu s in terview, whi ch i rt m s t c a s e s wa s ne yea r ( fr the 1 988- t 9 94 surveys ) r tw years ( fr the 1 996-200 0 s urvey s ). There were n mean s t ex te rn a l ly va l i d a te their re sp n ses. Our re sult s, t here f re, may b e s ubject t p ten t i a l inacc u racie s rela t ed t the inabil i ty f re spnden t s t reca l l i tf rma fln crrectly. A t the s ame t ime, t he NLS Y h a s advan tage s in t if s reg a rd cmpa re d t ther s e lf- re pr te d s u rveys in th a t the chr t ha d been s urveyed regtd a rly since 1 979 and t hu s wa s qui te fam i liar wi th the qne s t inn a i re, the re spn s e p rce s s, a nd the infrmatin reqnlred. Als, the NLSY was nt designed t be a survey ab u t wr k rela ted inj uri es an d i l lne s s e s r demanding wrk s chedule s-i t s p rimary bj ective wa s t eva l uate par t ic ip a n t s ' lng terln l abur m a rke t t ran s i t i ns a nd wa ge hi s try. The s u rvey t hus av i d s p rb l em s f infrmatin bias that typically plague attempts t ask injured wr ke r s ab u t their w rking c nditin s an d j b exp s u re s. Unl ike da ta s urce s re lated s pe c i fi ca lly t the field f ccupatinal safety and health, it is unlikely that respndents t the NLSY wi l l inte n t in a l ly r unin ten t ina l ly be a t t emp t ing t ju s t ify the legi t ima cy f a wrk related d i s rder, e s tablish i t s cmpens ab il i ty under wrke r s ' cm pen s a tin laws, r e s tabli sh t he emplyer' s cu lpabifiw fr the injury. Al l f th s e i s s ues a re unre la ted t t ire m a in cncern s f NL SY a n d thu s the d ata b ta ined pre sumably wil l b e le s s s u s cep t ib l e t cn tamina t i n by s u ch cnsi derat ins. s t reng th f th e s t udy i s i t s abili ty t cntr l fr the p ten t ial c n f und ing a ffects f.age, gender, cctlpa t i n, indus t ry, a n d r e g in. Hwever, many ther p ten t i a l cva r i a te s-s u ch a s wrke r s ' educa t in and incme levels, fami ly cmp s i t in, a nd heal th s ta t u s-we re n t cn s id e red fi x the an a lys i s, and thus their influence was n t a s s e s sed. Our m e th d s f r cn s idering the r i sks imp s ed by w rkers' ccupatin a nd th e emp l yer' s i ndu s try c l a s s ifica t in m ay have m a s ke d mre s ub t le d i ffe rence s re l a ted t pa r t icu l ar jb a s s ignmen t s w i thin a b ra der c cupa t i nal c las s ifica t i n r specific industry grup. B e ca u s e the s tu dy w a s ba s ed n s ecnd a ry an a ly s i s f exis t i ng na t in a l d a t, we we re a l s l imited in ur ab i l i ty t eva lu a te ther p t e n t ially imp r ta n t a spec t s f the dynamics un derlying the r i s k s f ln g wrk in g h u r s. Fr example, we d id nt have inf rm a t in ava i labl e n th e t ime f day the i nju ry cc urred, the kind s f j b act ivi tie s being pefrn e d, r th e s peci fi c cau se f the inj ury. Hwever, i nf rm a t in w s available abut the type f shift generally wrked n each jb ( day, nighb even ing, split, r rta t i ng s h i ft ) and thu s we were ab le t c nsider the influence f s h i ft wrk n injury risk and the cmbina t in a f fe c t f wrki n g b th a n uncnventina l shift s che du le a nd lng wrk i ng hurs. Th se r e s u l t s wi l l b e reprted in a separate publicatin. P l i cy i m p l i c a t i n s The ultimate reasn fr cnducting this research is t prevent ccupat inal injuries a nd i l lne s s e s, prm te vera l l w rke r hea l th, an d m inim i s e the adve r s e cn sequences t a ffe c ted wrkers. M s t au thri t ie s b e l i eve tha t e ffe c t ive p reve n t in f wrkplace inj u r ie s a nd i l lne s s e s requ i re s a multiface ted a pprach t ha t cmb ines cmprehe n s ive hazard identificat in a n d cn tr l, e rg nmic jb d e s ign, wrke r tra i n i ng, m e d i cal s u rve i l lance, cmpe te n t s upervi s i n, a nd a wrkp la ce cu l tu re and rg ani s a t in tha t p rm te s p t im a l sa fely a nd h eal th. The re s u l t s f t h i s s tu dy sug ge s t tha t sp ecial a t te n t in need s t b e paid t e s tabl i shing p r tective mea s u re s fr pepl e wrking ve r time. Fr ex ample, inten sive accid ent ha zard i d ent i fi cat in a n d cntrl p rcedure s ( fr example, per i d i c s a fe t y in spe c t ins ) cu ld be fcu s e d twa rd s j b s in which emplyee s wrk ver t ime schedu le s. O t her pltective appraches might include changes in wrk rganlsatin ( fr example, peri dic re s t bra ke s, rede si gning prce s s e s t avid the n eed f r vertime a s s ig nments, and emplying mre peple t wrk fewer hurs ea ch ), emplyer spn sred he a lth p rm t in p rgramme s ( f r examp le, cuns e l l i ng a n d e duca t i n abu t the r i sk s f lng w rk s chedul e s, pe ri d ic med i cal s u rve i l l ance examin a t ins f r " a t ri sk" w rkers, an d ergnmic red e s ign t d ecrea s e j b dem a n d s ), and in d ivi du a l cping and beh avittral p rac t ice s ( f r ex amp le, m a in tainin g gd s leep and nut ri t in, ge t t i ng d a i ly phys ical exerci s e a n d re gu lar medic a l care, avi d in g d ru g s a n d a l chl, an d s eeki ng WVWV. c c e r Yl]l ed. crn

5 96 De m b e, E r l k s n 0 De i b s, e i a i s uppr t ive s e rvice s wh en n eede d ). O ur s tu dy wa s nt a e d a t a s s e s s ing th e e ffec t ivene s s f the s e in terventins ha d ecrea s ing the r i sk f inj u ry, a nd a dd i t in a l re s earch i s nee ded in t h i s rega rd. AC K N OW L E D G E M E N T S "The aut h r s w u ld Rke t expzes s ur appreda d n t Rbert Re vi ll e, C a rl B igei w, Syl vi a Spencer, S imn F lkard, L il i e G lde n, G rdn S m i th, J a y H i m m e l s tein, a nd Rbin C l a rk f r the i r sugges t ins and a s s i s tance in t h i s s tudy. We a re i nd eb ted t R a l n e r Ne s s f r h i s tech n i cal expe r t i s e, wh ich inclu d e s s [O,va re an d te chnical s upp r t rela t ed t t h e P r Qu e s t d a taba s e s ys te m. Prel i m inary res u l t s f thi s s tudy were p re s ented a t m e e t ings f th e Ame ri can Pub l i c H e a I th A s sociat i n, t h e Na t inal Ins t i t u te f r O cc up a t i n a l S a fe ty a nd Heal th ( NIOSH), a n d the Na t i nal I n s t i t u te f r Ch i l d t teal th and Human Deve lpment. Th i s s t udy wa s cn d ucted wi th the s upp r t f a re search g ra nt ( #RO t OR07576 ) frm NIOSH. Au th rs' a f i l [a tl n s A E Demba, S M Banks, University f Massachusetts Medka[ Schl, U SA 1 g Erkksn, R G Delbas, Envirn Health gdences Institute, USA Cmpe t ing i n te res t s : T h i s s tudy wa s ba sed n sec nda ry a na lys i s f peb l ic }y ava i lable na t i na l s u rvey da ta a n d d id n t i n v lv e a ny dk : t cnlact w th human subjects. [t received an exemptin frm the insfitulina[ review bard at the Univ slly f Massachusegs Mnd cl Schd. The cndu c t F the s tudy and p re ra fin f th i s a dkb ha s invlved n cmpeting interesls fr any f the autbars. 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