Associat ion bet ween diast olic blood
pressure and cumulat ive work t ime
Asso c iaç ão e ntre p re ssão d iastó lic a
e te mp o d e se rviç o
1 Dep artam en to d e Saú d e Pú b lica , Un iv ersid a d e Est a d u a l Pa u list a . C. P. 543, Bot u ca t u , SP 18618- 970, Bra z il. cord eiro@fm b.u n esp .b r 2 Dep artam en to d e Ed u ca çã o M ot ora , Un iv ersid a d e Est a d u a l d e Ca m p in a s. C. P. 6134, Ca m p in a s, SP 13083- 970, Bra z il. eu clyd [email protected] n ica m p .b r Rica rd o Cord eiro 1
Eu clyd es Cu st ód io d e Lim a Filh o 2
Abst ract Dia st olic b lood p ressu re w a s v iew ed a s a gen eric in d ica t or of a gin g, a n d it s a ssocia -t ion w i-t h cu m u la-t iv e w ork -t im e w as s-t u d ied af-t er con -t rollin g for age as a p o-t en -t ial con fou n d in g fa ct or. T h e st u d y w a s con d u ct ed a m on g p rod u ct ion lin e w ork ers a t a Bra z ilia n t a n n ery in Ju ly 1993. T h e a ssocia t ion b et w een d ia st olic b lood p ressu re a n d cu m u la t iv e w ork t im e w a s v erified by fit t in g a secon d - ord er lin ea r regression m od el, w h ere d ia st olic b lood p ressu re w a s a fu n ct ion of w ork er’s a ge a n d cu m u la t iv e w ork t im e. By fit t in g t h e m od el, on e ca n p red ict t h a t , in t h e b egin n in g of w ork in g life a t t h e t a n n ery, on a v era ge ea ch 1 yea r p eriod is a ssocia t ed w it h a n in -crease of abou t 1.5 m m Hg in d iast olic blood p ressu re. Th e fit obt ain ed h igh ligh t s on e com p on en t d i rect ly a sso ci a t ed w i t h w o rk a s p a rt o f t h e ra t e o f p ressu re i n crea se i n t h e st u d y gro u p . T h i s com p on en t is t w ice as h igh as t h at d irect ly associat ed w it h age.
Key words Blood Pressu re; Hyp ert en sion ; Agin g; Occu p at ion al Healt h
Resumo A p ressã o a rt eria l d ia st ólica foi a n a lisa d a en q u a n t o in d ica d or gen érico d e en velh eci-m en t o, e su a associação coeci-m o t eeci-m p o d e serv iço foi est u d ad a ap ós o con t role d a id ad e coeci-m o p os-sív el fa t or d e con fu n d im en t o. O est u d o foi rea liz a d o en t re op erá rios d e u m cu rt u m e b ra sileiro em ju lh o d e 1993. Foi t est ad a a associação en t re p ressão d iast ólica e t em p o d e serv iço, aju st an d o u m m o d elo d e regressã o li n ea r d e segu n d a o rd em , em q u e a p ressã o d i a st ó li ca era f u n çã o d a id a d e e d o t em p o d e serv iço d o op erá rio. Ao a ju st a r o m od elo, p od e- se p rev er q u e, n o in ício d o t ra b a lh o n o cu rt u m e, em m éd ia , ca d a p eríod o d e u m a n o est á a ssocia d o com u m a u m en t o d e cerca d e 1,5 m m H g n a p ressã o d ia st ólica . O a ju st e ob t id o rea lça u m com p on en t e d iret a m en t e associad o ao t rabalh o com o p art e d o coeficien t e d e au m en t o d a p ressão n o gru p o est u d ad o. Esse com p on en t e é o d obro d aqu ele d iret am en t e associad o com a id ad e.
Introduction
Ca rd iova sc u la r d ise a se s h a ve b e e n id e n t ifie d a s t h e fir st c a u se o f d e a t h a m o n g wo r ke r s in Bra zil sin ce th e 1970s. High b lo o d p ressu re h a s b e e n t h e m a in r isk fa c t o r a m o n g t h e se d is e a se s. An in ve r se re la t io n sh ip b e t we e n o c c u -p a t io n a l q u a lifica t io n a n d b lo o d -p re ssu re h a s b e e n o b se r ve d a m o n g Bra zilia n wo rke rs (Co rd e iro e t a l., 1993). Th a t is t o sa y t h a t t h e h igh -e st p r-e va l-e n c-e o f h igh b lo o d p r-e ssu r-e is fo u n d a m o n g u n skille d in d u st r ia l wo r ke r s wit h t h e h e a vie st wo r k lo a d s a n d t h e lo we st in c o m e s. Th is c o r re la t io n su gge st s t h a t b lo o d p re ssu re m a y b e a n in d ica t o r o f p h ysica l we a r a n d t e a r a n d a gin g a m o n g in d u st r ia l wo rke r s. Th e a im of th e p resen t resea rch wa s to fu rth er th e stu d y of work-rela ted wea r a n d tea r a n d a gin g a m on g Bra zilia n workers. Dia stolic b lood p ressu re wa s vie we d a s a ge n e r ic in d ica t o r o f a gin g, a n d it s a sso c ia t io n wit h c u m u la t ive wo r k t im e wa s st u d ie d a ft e r co n t ro llin g a ge a s a co n fo u n d in g fa ctor.
Subject s and met hods
Th e resea rch wa s co n d u cted stu d yin g a ll o f th e 57 a ct ive p ro d u ct io n lin e wo rke rs a t a t a n n e r y in Bo tu ca tu , in th e Sta te of Sã o Pa u lo, Bra zil, in Ju ly 1993. Th e fa c t o r y p ro d u c e s le a t h e r fr o m ca t t le h id e s t h ro u gh a low-t e ch n o lo gy ch e m i-c a l p r o i-c e ss u sin g syn t h e t ii-c t a n n in g. Th e se wo rke rs h a d a lre a d y b e e n a n a lyze d in a cro ss-sectio n a l stu d y (Co rd eiro et a l., 1998), d isp la y-in g a h igh p re va le n ce o f a rte ria l h yp e rte n sio n . We a lso p resen ted d eta ils o n th e ta n n ery wo rk-e rs’ sm o kin g, a lco h o l in ta krk-e, b o d y m a ss in d rk-ex, a n d in c o m e a n d a c o m p a r iso n o f t h e ir b lo o d p re ssu re le ve ls t o t h o se o f o t h e r o ccu p a t io n a l gro u p s in Bra zil (Co rd eiro et a l., 1998).
Fo r t h e p re se n t st u d y, t h e wo r ke r s u n d e r -we n t a n o ccu p a t io n a l h ist o ry a n d b lo o d p re s-su re m e a s-su re m e n t s. Blo o d p re ss-su re (BP) wa s m e a su re d in t h e m o r n in g. Aft e r a 30- m in u t e rest p eriod in a silen t wa itin g room , th ree rea d -in gs we re t a ke n wit h -in t e r va ls o f a t le a st 15 m in u t e s. Me a su re m e n t s we re p e r fo r m e d o n t h e r igh t a r m wit h t h e in d ivid u a l in a s it t in g p o sitio n in a ll ca ses.
A fu lly ca lib ra t e d Ta ka o ka Mo d e l 203 m e r -cu r y ga u ge sp h ygm o m a n o m eter with a 26cm x 12cm a rm cu ff a n d a clin ica l ste th o sco p e we re u se d fo r a ll BP m e a su re m e n t s. Two h o u r s b e -fo re t h e fir st m e a su re m e n t t h e wo r ke r s we re a ske d t o e m p t y t h e ir b la d d e rs. Th e y we re a lso a sked n ot to sm oke or d r in k coffee or a n y oth er stim u la n t b evera ge from th is m om en t u n til th e
tests h ad b een com p leted . Blood p ressu re m ea -su rem en ts were m a d e b y th e sa m e fu lly tra in ed o rd e r ly. To m e a su re b lo o d p re ssu re, t h e a r m cu ff wa s in fla t e d ra p id ly u n t il t h e sp h ygm o -m an o-m eter reach ed 200 -m -m Hg. If, at th is p oin t, t h e re we re a u d ib le Ko ro t kow so u n d s, t h e a r m c u ff wa s fu r t h e r in fla t e d t o 260 m m H g. Th e a rm cu ff wa s th e n slowly d e fla te d . Th e systo lic a n d d ia st o lic b lo o d p re ssu re m e a su re m e n t s co rre sp o n d e d t o t h e re a d in g o n t h e sp h ygm o -m a n o -m e t e r a t t h e first a n d fift h p h a se s o f t h e Korotkow sou n d s, resp ectively. Th e scale on th e sp h ygm o m a n o m e t e r wa s gr a d u a t e d in 2 m il-lim e t e r d ivisio n s. Th e re a d in gs we re m a d e t o t h e n e a re st m illim e t e r. Th e lowe st o f t h e t h re e d ia st o lic b lo o d p re ssu re re a d in gs wa s u se d in th e a n a lysis. Cu m u la tive wo rk tim e a t th e ta n -n e r y wa s d ire ct ly a sse sse d b y i-n t e r vie ws wit h t h e st u d y gro u p a n d la t e r ra t ifie d b y co n su lt a -tio n in th e co m p a n y’s a d m in istra tive files.
Th e st u d y o f t h e a sso cia t io n b e t we e n d ia s-to lic b lo o d p ressu re a n d cu m u la tive wo rk tim e wa s p e r fo r m e d b y fit t in g a c o m p le t e se c o n d -o rd e r lin e a r re gre ssi-o n m -o d e l, wh e re d ia st -o lic b lo o d p re ssu re wa s a fu n ct io n o f t h e in d e p e n -d e n t va r ia b le s wo r ke r’s a ge a n -d c u m u la t ive wo rk tim e, a s sh own in th e eq u a tio n b elow:
d BPi= α+ β1Ai+ β2Ti+ β3Ai2+ β4Ti2+ β5AiTi
+ εi(1)
wh e re ‘A’ st a n d s fo r wo r ke r’s a ge a n d ‘T’ sta n d s fo r wo rker’s cu m u la tive tim e a t th e ta n n ery. Th e co sin e o f th e a n gle b etween th e sa m -p le ve ct o rs A a n d T wa s u se d a s a n e st im a t e o f co llin ea rity b etween wo rker’s a ge a n d cu m u la -t ive wo r k -t im e in -t h e s-t u d y gr o u p . Th is a n gle wa s e va lu a t e d u sin g t h e co e fficie n t o f sa m p le c o r re la t io n (r2AT), a n d t h e va r ia n c e in fla t io n
fa ct o r [(1-r2AT)-1] ( We isb e rg, 1985). Th e co n d
i-t io n n u m b e r k [(la r ge si-t e ige n va lu e / sm a lle si-t e ige n va lu e )1/ 2] ( We t h e r il, 1986) wa s a lso u se d
a s a d d itio n a l in fo rm a tio n . Th ese a n a lyses were ju st ifie d d u e t o t h e p o ssib ilit y o f c o r re la t io n b etween th e wo rker’s a ge a n d cu m u la tive wo rk t im e in a give n gr o u p o f wo r ke r s, m a kin g t h e p ro p o sed fit d ifficu lt (Belsley, 1991).
Ca lc u la t io n s we re p e r fo r m e d u sin g t h e CORRa n d REGp ro ce d u re s o f th e SAS fo r Win -d ows 6.12 so ftwa re.
Result s
Figu re s 1, 2, a n d 3 sh ow, re sp e ctive ly, d ia sto lic b lo o d p re ssu re, wo rke r’s a ge, a n d c u m u la t ive wo rk tim e d istrib u tio n s fo r th e stu d y gro u p.
Up on fittin g th e m od el rep resen ted in eq u a -t io n (1) b y -t h e s-t e p wise m e -t h o d , we o b se r ve d t h a t t h e co e fficie n t sβ3a n d β5p re se n t e d a
sig-n ificasig-n ce level h igh er th asig-n 0.15. Th u s, th e term s β3Ai2e β5AiTiwe re e xc lu d e d fr o m t h e m o d e l,
wh ich b eco m es:
d BPi= α+ β1Ai+ β2Ti+ β3T2+ εi(2).
Ta b le 2 sh ows th e sta tistics o b ta in ed b y fit-tin g th is red u ced m o d el.
Figu re s 4, 5, a n d 6 sh ow t h e jo in t d ist r ib u tio n o f re sid u a ls o f th e fitte d re gre ssio n (e q u a -t io n 2), a n d p re d ic-t e d va lu e, wo rke r’s a ge, a n d cu m u la tive wo rk tim e, resp ectively.
Ta b le 3 sh ows th e sta tistics o b ta in ed b y fit-t in g e q u a fit-t io n (2) wh e n a p p lie d fit-t o fit-t h e sfit-t u d y gro u p d a t a a ft e r e xc lu sio n o f t wo wo r ke r s wh o se b lo o d p re ssu re va lu e s we re co n sid e re d o u tliers, a s d iscu ssed b elow.
Discussion
St u d yin g t h e a sso cia t io n b e t we e n b lo o d p re s-su re a n d cu m u la tive wo rk tim e is u s-su a lly d iffi-c u lt d u e t o t h e p r o b le m s o f iffi-c o n t r o llin g a ge c o n fo u n d in g u sin g m u lt ip le re gre ssio n . Th is fa ct is d u e to th e co llin ea rity th a t u su a lly exists b e twe e n th e va ria b le s wo rke r’s a ge a n d cu m u -la t ive wo rk t im e, wh ich in cre a se s t h e va ria n ce o f e st im a t e s o b t a in e d wit h re gre ssio n m o d e ls. However, in th is p articu lar set of d ata, collin ea r-ity wa s n ot im p orta n t a s sh own by th e sta tistics in Ta b le 1. Th is o c c u r re d b e c a u se , a lt h o u gh m e m b e r s o f t h e st u d y gr o u p we re lo n g- t e r m e m p loye e s, t h e a ge a t wh ich t h e y b e ga n wo rk a t t h e t a n n e r y va r ie d gre a t ly, a s sh own in Fig-u re 7. Fo r th is rea so n , th e stFig-u d y gro Fig-u p p resen t-ed a grea t n u m b er o f o ld er wo rkers with sh o rt-er cu m u la tive wo rk tim es.
It is im p o rta n t to n o te th a t wh en fittin g th e m o d el (1), th e h igh p -va lu e a sso cia ted with th e term β5AiTim a y b e p a rtia lly d u e to th e rela
tive-ly sm a ll n u m b er o f su b jects stu d ied .
Th e fit o f t h e fin a l m o d e l re ve a le d a n a sso -c ia t io n b e t we e n d ia st o li-c b lo o d p re ssu re a n d c u m u la t ive wo rk t im e , a ft e r c o n t r o llin g a ge co n fo u n d in g, a s sh own in Ta b le 2.
Two p o in t s re la t in g t o t wo wo r ke r s wh o se d ia st o lic b lo o d p re ssu re wa s u n u su a lly h igh were h igh ligh ted a n a lyzin g figu re s (4), (5), a n d (6). We o b se r ve d t h a t t h e se wo r ke r s h a d t h e first a n d th ird h igh est b lo o d p ressu re va lu es o f th e gro u p, with rela tively low a ge a n d sh o rt cu -m u la t ive wo rk t i-m e. Aft e r a n a -m n e sis, t h e t wo wo rke rs we re fo u n d to h a ve fa m ily h isto rie s o f h igh b lo o d p re ssu re a n d we re e xc lu d e d fro m th e a n a lysis. Up o n re a d ju stin g th e m o d e l a fte r t h is e xc lu sio n , a b e t t e r fit wa s o b t a in e d , a s
Fig ure 1
Distrib utio n o f stud y p o p ulatio n ac c o rd ing to d iasto lic b lo o d p re ssure .
0 % 5 10 15 20 25 30 35
[120-130) diasto lic b lo o d pre ssure (mmHg ) [110-120) [100-110) [90-100) [80-90) [70-80) [60-70)
Fig ure 2
Distrib utio n o f stud y p o p ulatio n ac c o rd ing to ag e .
% 0 5 10 15 20 25 30 35
[60-70) ag e rang e (ye ars) [50-60)
[40-50) [30-40)
sh own b y t h e c o m p a r iso n b e t we e n Ta b le s 2 a n d 3. By refittin g th e m od el a fter th e exclu sion o f t h e t wo o u t lie r s, o n e c a n p re d ic t t h e d ia stolic b lood p ressu re of th e stu d y grou p, a ccord -in g to th e eq u a tio n b elow ( Ta b le 3):
`
d BPi= 54.01 + 0.59Ai+ 0.92Ti- 0.03T2(3)
Th u s, fr o m t h e re a d ju st e d m o d e l, we o b -served th a t in th e stu d y grou p, in th e b egin n in g o f wo rkin g life a t th e ta n n ery, ea ch 1-yea r p erio d is a sserio c ia t e d wit h a m e a n in c re a se erio f a p -p ro xim a t e ly 1.5 m m H g in t h e d ia st o lic b lo o d p re ssu re. Ab o u t t wo t h ird s o f t h is in c re a se [0.92/ (0.92+0.59)] is d ire c t ly a sso c ia t e d wit h t h e wo rk q u a n t ifie d b y cu m u la t ive t im e a t t h e tan n ery. In oth er word s, th e fit allows u s to id en -tify a co m p o n en t d irectly a sso cia ted with wo rk a s p a rt o f th e ra te o f b lo o d p ressu re in crea se in t h e st u d y gr o u p . Th is c o m p o n e n t is t wic e a s h igh a s th a t d irectly a sso cia ted with a ge.
Two h yp o t h e se s ca n b e p r o p o se d t o in t e r p ret th e m ean in g of th e q u ad ratic term of eq u a -tion (3), -0.03Ti2. Th e first is th a t it cou ld b e th e
resu lt of th e h igh er sen sitivity of workers to oc-c u p a t io n a l st re sso r s a t t h e b e gin n in g o f t h e ir work life a t th e ta n n er y, i.e. wh en th ey h a ve still n o t d e ve lo p e d d e fe n se st ra t e gie s a ga in st t h e a ggre ssio n fro m t h e n e w o ccu p a t io n . Th e se c-o n d is t h a t sc-o m e c-o f t h e c-o ld e r wc-o r ke r s wit h a lo n ge r c u m u la t ive wo rk t im e a t t h e t a n n e r y m a y b e lea vin g th eir jo b s d u e to co m p lica tio n s c a u s e d b y h igh b lo o d p re s s u re , a h yp o t h e s is re la te d to th e h e a lth y wo rk e ffe ct (McMich a e l, 1975). In t h is c a se , t h e q u a d r a t ic t e r m wo u ld b e t h e r e su lt o f a lim it a t io n o f t h e st u d y d e -sign .
Th e seco n d o f th ese two h yp o th eses is co r -ro b o ra ted by a ch ievin g a good fit of th e sim p li-fied m od el b elow (with ou t th e q u a d ra tic term ),
d BPi= α+ β1Ai+ β2Ti+ εi(4),
wh en a p p lied to a su b set of th e stu d y gr ou p co n sist in g o f wo rke rs wit h sh o r t e r cu m u la t ive work tim es.
Ta b le 4 sh ows t h e st u d y o f co llin e a r it y b e -t we e n a ge a n d c u m u la -t ive wo rk -t im e a p p lie d t o t h o se wo rke rs wh o se cu m u la t ive wo rk t im e wa s less th a n or eq u a l to 21 yea rs, a n d a fter th e e xclu sio n o f t h e t wo o u t lie r s p re vio u sly m e n -t io n e d . Ta b le 5 sh ows -t h e sim p lifie d m o d e l (4) a p p lie d t o t h is sa m e su b gr o u p . A b e t t e r fit is o b ta in e d in co m p a r iso n to th a t p re vio u sly o b -t a in e d (e q u a -t io n 2), wi-t h a re la -t ive ly h igh r2
va lu e, a s sh own in Ta b le 5. Th is 21-yea r cu t-o ff p o in t wh ich o p tim ize s th e fit o f th e m o d e l wa s a n a c c id e n t a l fin d in g. Mo d e l (4) is we ll fit t e d wh e n t h e c u t - o ff p o in t r a n ge s fr o m 18 t o 23 yea rs, a ch ievin g its b est fit wh en th e va lu e is 21 yea rs.
It is in t e re st in g t h a t n o a sso c ia t io n wa s fo u n d b etween systo lic b lo o d p ressu re a n d cu -m u la tive wo rk ti-m e by fittin g -m o d els si-m ila r to m o d e l (2) a n d (4), e it h e r in t h e st u d y gr o u p a s a wh o le o r in a n y o f its su b sets.
Fin a lly, th e a ssocia tion b etween cu m u la tive wo rk t im e a n d d ia st o lic b lo o d p re ssu re sh own h e re su ggests th a t cu m u la tive wo rk tim e a cte d a s a m a rke r o f e xp o su re t o sit u a t io n s t h a t m igh t c a u se a h igh e r in c re a se in b lo o d p re s-su re o f t h e wo r ke r s u n d e r st u d y. Th is wo u ld p rovid e a st im u lu s fo r t h e se a rch fo r b o t h t h is a sso cia tio n in o th er gro u p s o f wo rkers a n d th e ca u sa l rela tio n s b etween o ccu p a tio n a n d d ia s-to lic b lo o d p ressu re.
Fig ure 3
Distrib utio n o f stud y p o p ulatio n ac c o rd ing to c umulative wo rk time at tanne ry.
0 % 5 10 15 20 25
[35-40) cumulative wo rk time (ye ars) [30-35) [25-30) [20-25) [15-20) [10-15) [5-10) [0-5)
Tab le 1
Statistic s o b taine d fro m the stud y o f c o lline arity b e twe e n ag e (A) and c umulative wo rk time at tanne ry (T).
r2AT (1-r2AT)-1 k
0.3765 1.6038 16.4160
r2AT: sq uare o f Pe arso n’s c o e ffic ie nt o f c o rre latio n b e twe e n A and T. (1-r2AT)-1: varianc e inflatio n fac to r.
Tab le 2
Estimate s and statistic s o b taine d b y fitting the re g re ssio n mo d e l d BPi=α+ β1Ai+ β2Ti+ β3Ti2+ εi
to the stud y p o p ulatio n.
paramet er paramet er est imat es st andard error T for H0: paramet er = 0 Prob > |T|
α 58.805 7.665 7.672 0.0001
β1 0.493 0.178 2.774 0.0076
β2 1.080 0.587 1.841 0.0713
β3 -0.036 0.016 -2.224 0.0305
r2= 0.22 F = 5.081
d e g re e s o f fre e d o m = 56
Fig ure 4
Jo int d istrib utio n o f the variab le s re sid ual o f the mo d e l d BP`i= a + biAi+ b2Ti+ b3Ti2and p re d ic te d value .
70 80 90 100 p re d ict value
(mmHg ) -40
-30 -20 -10 0 10 20 30 40
re
si
d
u
a
Fig ure 5
Jo int d istrib utio n o f the variab le s re sid ual o f the mo d e l
`
d BPi= a + biAi+ b2Ti+ b3Ti2and c umulative wo rk time
at tanne ry.
0 cumulative wo rk
time (ye ars) -40
-30 -20 -10 0 10 20 30 40
re
si
d
u
a
l
10 20 30 40
Fig ure 6
Jo int d istrib utio n o f the variab le s re sid ual o f the mo d e l d BP`i= a + biAi+ b2Ti+ b3Ti2and ag e .
ag e (ye ars) -40
-30 -20 -10 0 10 20 30 40
re
si
d
u
a
l
Tab le 3
Estimate s and statistic s o b taine d b y fitting the re g re ssio n mo d e l d BPi=α+ β1Ai+ β2Ti+ β3Ti2+ εi
to the stud y p o p ulatio n afte r e xc lusio n o f two o utlie rs.
paramet er paramet er est imat es st andard error T for H0: paramet er = 0 Prob > |T|
α 54.008 6.633 8.142 0.0001
β1 0.587 0.152 3.867 0.0003
β2 0.923 0.502 1.838 0.0720
β3 -0.031 0.014 -2.279 0.0269
r2= 0.32 F = 8.297
d e g re e s o f fre e d o m = 54
Fig ure 7
Distrib utio n o f stud y p o p ulatio n ac c o rd ing to ag e at whic h wo rke rs e nte re d the tanne ry.
0 %
5 10 15 20 25
[60-65) ag e rang e (ye ars) [55-60)
[50-55) [45-50)
[40-45) [35-40)
[30-35) [25-30)
[20-25) [15-20)
Tab le 4
Statistic s o b taine d fro m the stud y o f c o lline arity b e twe e n ag e (A) and c umulative wo rk time at tanne ry (T) ap p lie d to wo rke rs with c umulative wo rk time le ss than o r e q ual to 21 ye ars.
r2AT (1-r2AT)-1 k
0.2272 1.2940 10.5234
r2AT: sq uare o f Pe arso n’s c o e ffic ie nt o f c o rre latio n b e twe e n A and T. (1-r2AT)-1: varianc e inflatio n fac to r.
References
BELSLEY, D. A., 1991. Con d it ion in g Dia gn ost ic – Collin ea rit y a n d W ea k Da t a in Regression. Ne w York: Joh n Wiley & Son s.
CORDEIRO, R.; FISCH ER, F. M.; LIMA FILH O, E. C. & MOREIRA FILH O, D. C., 1993. Ocu p a çã o e h ip er-ten sã o. Revista d e Saú d e Pú blica, 27:380-387. CORDEIRO, R.; LIMA FILH O; E. C. & ALMEIDA, I. M.,
1998. Pre ssã o a r te ria l e n tre tra b a lh a d o re s d e u m cu rtu m e. Revista d e Saú d e Pú blica. 32: 467-476.
McMICHAEL, A. J., 1975. Ob serva tion s on th e eva lu a -t io n o f o c c u p a -t io n a l m o r-t a li-t y d a -t a . Jou rn a l of Occu p ation al Med icin e, 17:128-131.
WEISBERG, S., 1985. Ap p lied Lin ear Regression. Ne w York: Joh n Wiley & Son s.
WETHERILL, G. B., 1986. Regression An alysis w ith Ap -p lication s. Ca m b rid ge: Ch a p m a n a n d Ha ll.
Tab le 5
Estimate s and statistic s o b taine d b y fitting the re g re ssio n mo d e l d BPi=α+ β1Ai+ β2Ti+ β3Ti2+ εi
to wo rke rs with c umulative wo rk time le ss than o r e q ual to 21 ye ars afte r e xc lusio n o f 2 o utlie rs.
paramet er paramet er est imat es st andard error T for H0: paramet er = 0 Prob > |T|
α 53.712 6.667 8.057 0.0001
β1 0.590 0.164 3.605 0.0010
β2 0.599 0.271 2.211 0.0339
r2= 0.49 F = 16.484
