ergonomisk risikovurdering · making the assessment. if a job consists of a variety of tasks, each...
TRANSCRIPT
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Ergonomisk risikovurdering: hvordan gjøre det med æren i behold?
Svend Erik Mathiassen Centrum för belastningsskadeforskning
Högskolan i Gävle
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* För osmarta
* För dyra
* För begränsade
Riskvärderingar bygger ofta på
observationer av fysisk belastning
som är …
* För osystematiska
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Bättre metoder för riskbedömning – Varför är det viktigt?
• Klokare tolkning av insamlade belastningsdata
• Självkritik inför ergonomiska undersökningar
• Bättre resursutnyttjande vid ergonomiska undersökningar
Vart kan det leda?
• Tydligare kvalitetskrav på ergonomisk dokumentation
• Manualer för kvalitetssäkrad bedömning av belastningsdata
• Instrument för uppföljning av systematiskt arbetsmiljöarbete
Trovärdighet…
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Bra riskbedömning
kräver
Bra data om
belastningar
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Vilket mätinstrument
ska jag välja
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Metoder för belastningsbedömning
Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Tro
vä
rdig
he
t Enke
lhet
Fle
xib
ilitet
Pris
Winkel & Mathiassen, 1994
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Systematic evaluation of observational
methods assessing biomechanical
exposures at work
Takala EP, Pehkonen I, Forsman M, Hansson GÅ,
Mathiassen SE, Neumann P, Sjøgaard G,
Veiersted KB, Westgaard R, Winkel J
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Quick Exposure Check…
“At least one complete work cycle is observed before
making the assessment. If a job consists of a variety of
tasks, each task can be assessed separately.”
David et al., 2008
Observer’s assessment Worker’s assessment
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Quick Exposure Check… David et al., 2008
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Strain Index… “The simplest analysis, described here, occurs when the job involves a
single task and the intensities and postures for each hand exertion are
approximately equal.”
Moore et al., 1995 / 2005
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NIOSH lifting equation… Waters et al., 1993
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NIOSH lifting equation… Waters et al., 1993
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Vad kom vi fram till?
* 30 olika metoder
– 15 för belastning allmänt
– 9 för nacke / skuldror / arm
– 8 för manuell hantering
* Stora skillnader i kvantitet och kvalitet av
forskningen om enskilda metoders prestanda
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Metoder för bedömning av nacke/skulder/arm
Metod Samstäm m
bättre metod
Samband m
besvär
Samstäm
inom obs
Samstäm
mellan obs
Användare
HSE UL - - - - P, A(?)
RULA Moderat-Låg X - God-Mod? P, F
Stetson's checklist - - - Moderat F
Keyserling's Cumulative
trauma checklist
Moderat - - Mod-Låg P, F
Ketola's expert tool Moderat-Låg - - Moderat P
Strain index (SI) Moderat X God-Mod God-Mod P, F
ACGIH HAL Moderat X God Moderat P, F
OCRA Moderat X - - P, F
Washington state
ergonomic rule
- X - Moderat P, A(?)
P; praktiker, ergonomer. F; forskare. A; arbetare
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Metoder för bedömning av manuell hantering
Metod Samstäm m
bättre metod
Samband m
besvär
Samstäm
inom obs
Samstäm
mellan obs
Användare
NIOSH Lifting Equation Ej relevant X - - P, F
Arbouw Moderat - - - P
NZ Code for MH - - - - P
ManTRA - - - - P, F(?), A(?)
MAC - - God-Mod God-Mod P, A(?)
Washington state
ergonomic rule
Moderat X - Moderat P, A(?)
ACGIH Lifting TLV Moderat - - - P
BackEST Moderat-Låg - - Moderat F
P; praktiker, ergonomer. F; forskare. A; arbetare
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* Får problem när olika uppgifter kombineras i ett arbete
* Fokuserar individen, inte systemet
* Tar sällan hänsyn till exponeringens tidsförlopp och då oftast i form av genomsnittsfrekvens
* Visar endast indirekt på förändringsmöjligheter
Befintliga riskvärderingsinstrument…
* Inkluderar sällan bruksanvisning / datainsamlingsprinciper
* Är svåra att koppla till produktionsvillkor
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* Systematiska observationsmetoder
Att observera fysisk belastning med hedern i behåll…
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Hur säkert
är resultatet
av min datainsamling
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Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Tro
vä
rdig
he
t Enke
lhet
Fle
xib
ilitet
Pris
Metoder för belastningsbedömning
Winkel & Mathiassen, 1994
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Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Tro
vä
rdig
he
t
Metoder för belastningsbedömning
Winkel & Mathiassen, 1994
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What’s the problem –
en industriarbetares arbetsdag…
registrering
registrering
Andel tid då ryggen är böjd mera än 20°
Minuter
25
50
75
100 200 300 400 500
0
0
100
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0
90
100
60
40
20
10
80
70
50
30
0 5 10
Framåtböjning
i ryggen hos
industriarbetare
%
5-percentil
median
95-percentil
What’s the problem…
%tid över 20°
median
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Tid (procent) med höger överarm över 60°
Frisör nr.
1 28 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
18
16
14
12
10
8
6
4
2
0
Variabilitet mellan frisörer och arbetsdagar
Wahlström et al., 2010
Frisörens medelvärde
Enskilda dagar
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Variabilitet i belastning
inom och mellan individer
ger osäkra stickprov
(dvs. information som inte är perfekt)
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√ s2BS/ns+s2
BD/nsnd
Precision / Information
Varianskomponenter
Antal mätningar
(Kvalitet av) information: 1/SD
Uttryck för precision av ett estimat av
medelbelastning:
Varians eller Standarddeviation (SD)
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Mer data ger bättre säkerhet
Paquet et al., 2005
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Variabilitet i belastning
inom och mellan individer
ger osäkra stickprov
Mer data
ger bättre säkerhet
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Hur mycket data
behöver jag
för att nå ett resultat
som är tillräckligt
säkert
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och efter
En industriarbetares arbetsdag
100
efter
innan YES!
innan
efter Neeej…
före en lyckad förändring…
Andel tid (procent) med ryggen böjd mera än 20°
Minuter
25
50
75
100 200 300 400 500
0
0
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3 industriarbetare
16 videofilmer per person från olika dagar, 3min per film
1 observatör
Markering när ländryggen framåtböjd >20°
Material –
Mathiassen & Paquet, 2010
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Lyckade interventioner mot böjda ryggar
Mathiassen & Paquet, 2010
Övre 1/8 ändrat med:
10% 50%
0 10 20 30 40 50 60
20
0
40
60
80
100
%
Innan intervention
Tid >20°
100
50% 10%
Övre 1/2 ändrat med:
0 10 20 30 40 50 60
%
20
0
40
60
80
Innan intervention
Tid >20°
Fördelning av belastning för én person
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Sannolikheten att upptäcka
att interventionen haft effekt…
Högsta 1/8 minskat med:
10%
Antal mätningar före och efter
0.6
0.5
0.7
0.8
0.9
1.0
2 4 6 8 10 1 3 5 7 9
Mathiassen & Paquet, 2010
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Sannolikheten att upptäcka
att interventionen haft effekt…
Högsta 1/8 minskat med:
10%
Antal mätningar före och efter
0.6
0.5
0.7
0.8
0.9
1.0
2 4 6 8 10 1 3 5 7 9
Mathiassen & Paquet, 2010
~ 15 minuter
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Sannolikheten att upptäcka
att interventionen haft effekt…
Högsta 1/8 minskat med:
10% 50%
Högsta 1/2 minskat med:
… är låg, om inte
ändringen är rejäl och
man har många mätningar
Antal mätningar före och efter
0.6
0.5
0.7
0.8
0.9
1.0
2 4 6 8 10 1 3 5 7 9
Mathiassen & Paquet, 2010
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* Tillräckligt mycket data för att ge användbar information
* Systematiska observationsmetoder
Att observera fysisk belastning med hedern i behåll…
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Hur fördelar jag
ett antal mätningar
så att jag får
mest möjlig information
- Mellan individer, dagar,
perioder inom dag
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Många individer
Många dagar per individ
Det är lika effektivt
Fördela10 mätdagar mellan10 individer –
vad är statistiskt mest effektivt
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antal individer 0 5 10 15 20
95%
PI,
%m
edel
0
10
20
30
40
dagartotal: 10
Fördelning av mätdagar
medel: 23°
varBS: 14
varBD: 35
Frisörer, armelevation
dagartotal: 20
95%PI: 95% av alla estimat ligger inom detta avstånd från medelvärdet
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Hur fördelar jag
ett antal mätningar
så att jag får
mest möjlig information
- Mellan individer, dagar,
perioder inom dag
- Över tid inom dag
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60 minuters registrering
i ett block
registrering
registrering
Andel tid (procent) med höger arm över 90°
Minuter
25
50
75
100 200 300 400 500
0
0
100
Mätningar inom en dag…
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60 minuters registrering
i två block Andel tid (procent) med höger arm över 90°
Minuter
25
50
75
100 200 300 400 500
0
0
100
registrering
registrering
Mätningar inom en dag…
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Én lång period
Flera korta perioder under dagen
Det spelar ingen roll
Fördela 60 minuters datainsamling under
en hel arbetsdag – vad är mest effektivt
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23 bilmekaniker
4 hela arbetspass
Inklinometri, överarmsvinkel
Tid >90°
Datamaterial
Liv et al., 2011
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Fördelning av mätningar över tid
5
Blockstorlek
Teoretisk
prestanda
Sämre
Liv et al., 2011
Total registreringstid (minuter)
60 120 240
15
30
60
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Rela
tiv v
arian
s p
å m
ed
elv
ärd
et
s2BS/ns+s2
BD/nsnd+s2WD/nsndnq
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60 120 240
Total registreringstid (minuter)
Liv et al., 2011
0.0
0.5
1.0
1.5
2.0
2.5
3.0
5
Blockstorlek
15
30
60
Sprid ut
mätningarna !
- särskilt när
totaltiden är kort
[fixed-interval
aningen bättre
än random]
Fördelning av mätningar över tid R
ela
tiv v
arian
s p
å m
ed
elv
ärd
et
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* Smart upplagda mätningar
* Tillräckligt mycket data för att ge användbar information
* Systematiska observationsmetoder
Att observera fysisk belastning med hedern i behåll…
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… och mätningar kostar
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Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Tro
vä
rdig
he
t Enke
lhet
Fle
xib
ilitet
Pris
Metoder för belastningsbedömning
Winkel & Mathiassen, 1994
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Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Pris
Metoder för belastningsbedömning
Winkel & Mathiassen, 1994
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Vad kostar en studie…
Trask et al., 2012; Trask et al., 2013
ČA ČA+ČR ČA+ČR+ČE ČA+ČR+ČE+ČS ČA+ČR+ČE+ČS+ĊT ČA+ČR+ČE+ČS+ĊT+ĊV ČA+ČR+ČE+ČS+ĊT+ĊV+ĊH ČA+ČR+ČE+ČS+ĊT+ĊV+ĊH+ĊR ČA+ČR+ČE+ČS+ĊT+ĊV+ĊH+ĊR+ĊD ČA+ČR+ČE+ČS+ĊT+ĊV+ĊH+ĊR+ĊD+ĊM
Fasta kostnader
Rörliga kostnader
ČA+ČR+ČE+ČS+ĊT+ĊV+ĊH+ĊR+ĊD+ĊM
Administration och möten Administration och möten
Rekrytering av studieföretag
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Hotellövernattningar
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Hotellövernattningar
Rekrytering av mätpersoner
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Hotellövernattningar
Rekrytering av mätpersoner
Datainsamling
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Hotellövernattningar
Rekrytering av mätpersoner
Datainsamling
Databearbetning
Administration och möten
Rekrytering av studieföretag
Inköp av utrustning
Utveckling mjukvara
Träning av personal
Resor till mätställe
Hotellövernattningar
Rekrytering av mätpersoner
Datainsamling
Databearbetning
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Vad kostar en studie… Flygplanslastare, 81 hela dagar,
arm- och rygglutning
Euro Videoobservation Inklinometri
Datainsamling, fasta 17,209 22,228
Datainsamling, rörliga 38,160 44,428
Datainsamling, total 55,369 66,656
Databearbetning, fasta 20,363 24,283
Databearbetning, rörliga 11,070 1,972
Databearbetning, total 31,433 26,255
Total kostnad 86,802 92,912
Trask et al., 2012; Trask et al., 2013
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Objektiva
Teknisk mätning
Observation
Subjektiva
Intervju
Enkät
Dagbok
Special
Register
Tro
vä
rdig
he
t
Pris
Metoder för belastningsbedömning
Winkel & Mathiassen, 1994
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Kvalitén av information
vid en viss budget
eller
Priset för information
av en viss kvalitet
Kostnadseffektivitet:
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Studier som jämför kostnadseffektiviteten
av olika sätt att samla in data
• Armstrong 1995, 1996
• Lemasters et al. 1996
• Shukla et al. 2005
• Rezagholi et al. 2012
• Mathiassen et al. 2013
• Trask et al. 2014
Rezagholi & Mathiassen, 2010; uppdaterat
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Arbetet har filmats
på video.
Vilket är
det smartaste sättet
att observera
arbetsställningar
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Observatörer skiljer sig åt i bedömning…
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En observatör är inte överens med sig själv …
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Vad är mest kostnadseffektivt vid
observation av arbetsställningar -
Observera filmsekvenser
Observera stillbilder
Det är ingen skillnad
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5 frisörer
Två 30-min videofilmer från olika dagar
4 observatörer
Skattad överarmsvinkel
2 repetitioner
Videoobservation av arbetsställning –
Rezagholi et al., 2012
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15 utspridda snapshots
120 utspridda snapshots
15 sekvenser à 2 min
120 sekvenser à 15 sek
Fyra sätt att observera 30 min video –
Rezagholi et al., 2012
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Varians inom och mellan observatörer*…
… och observationstid per film
120
sekvenser
15
sekvenser
120
snapshots
15
snapshots
Varians:
Mellan observatörer 43 116 87 244
Inom observatör 149 143 131 290
Arbetstid* (minuter):
Observation 73 39 18 2
* 30 min film, andel tid under 15°
Rezagholi et al., 2012
Spridda snapshots: största variabiliteten,
men bästa kostnadseffektiviteten !
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Hur ska jag prioritera
min arbetstid:
filma arbetet
eller observera
de film jag har
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Många videofilmer
Många observatörer
Många observationer per observatör
Vad är mest kostnadseffektivt vid
observation av arbetsställningar -
Det är ingen skillnad
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Enhetskostnader
Kostnad:
CFnd+COndnonr
Kostnad vs information
Informationens kvalitet:
1/√s2WS/nd+s2
BO/no+s2WO/ndnonr
Varianskomponenter Antal mätningar
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CF; Filmning:
Transport och filmning
Kostnadskalkyl – arbetstid
CO; Observation:
Titta och bedöma
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Källor till osäkerhet i observationer
av arbetsställningar
• Skillnader mellan observatörer
- observatörer bedömer inte arbetsställningar lika
• Skillnader inom observatör
- en enskild observatör är inte konsekvent
• ”Biologisk” varians
- en observerad individ gör olika saker vid olika
tidpunkter
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5 frisörer
Två 30-min videofilmer från olika dagar
4 observatörer
120 snapshots per video
Skattad överarmsvinkel
Tid >90°
2 repetitioner
Observatörsvarians –
och <15°
Mathiassen et al., 2013
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28 frisörer
4 hela arbetspass
Inklinometri, överarmsvinkel
Tid >90° och <15°
Biologisk varians
Mathiassen et al., 2013
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Varianskomponenter och enhetskostnader
%tid <15°
Varianskomponenter:
Inom frisör s2WS 179.6
Mellan observatörer s2BO 87.0
Inom observatör s2WO 130.6
Enhetskostnader:
Filmning, € CF 36
Observation, € CO 7
Rezagholi et al., 2012
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Grytklara ekvationer –
Kostnad:
36nd+7ndnonr
Informationens kvalitet:
1/√179.6/nd+87.0/no+130.6/ndnonr
Mathiassen et al., 2013
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Value for the money –
tid med armen <15°
0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Kostnad, €
0.20
0.15
0.10
0.05
0.00
Info
rmationen
s k
valit
et
(1/S
D)
1Obs 1Rep
1
3 2
5 4 10 9 8 7 6
12 14 16 18 20 22 # videos
Mathiassen et al., 2013
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0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Kostnad, €
0.20
0.15
0.10
0.05
0.00
1Obs 1Rep
4Obs 1Rep
600 € lagt på att 1 observatör
bedömer 14 videofilmer én gång
ger 36% sämre information
Value for the money –
tid med armen <15°
Mathiassen et al., 2013
Info
rmationen
s k
valit
et
(1/S
D)
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0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Kostnad, €
0.20
0.15
0.10
0.05
0.00
1Obs 1Rep
4Obs 1Rep
Money for the value –
tid med armen <15°
En information av storleken 0.10
kostar 415% mer om 1 observatör
bedömer 23 videofilmer én gång
Mathiassen et al., 2013
Info
rmationen
s k
valit
et
(1/S
D)
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Från jämförelser
till optimering…
För en viss budget, vad är den maximala
kvalitén av information som kan uppnås?
eller
Vid ett visst krav på informationens kvalitet,
vilket är den billigaste sättet att nå dit?
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Literatur om kostnadseffektiv datainsamling
Jämförelser • Armstrong 1995, 1996
• Lemasters et al. 1996
• Shukla et al. 2005
• Rezagholi et al. 2012
• Mathiassen et al. 2013
• Trask et al. 2014
Rezagholi and Mathiassen, 2010; updated
• Spiegelman & Gray 1991
• Spiegelman 1994
• Stram et al. 1995
• Duan & Mage 1997
• Allison et al. 1997
• Foster & Asztalos 2001
• Whitmore et al. 2005
• Mathiassen & Bolin 2011
Optimering
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Kostnad:
CFnd+COndnonr
Optimering av kostnadseffektivitet
Informationens kvalitet:
1/√s2WS/nd+s2
BO/no+s2WO/ndnonr
… bestäm den kombination (nd,no,nr)
som,vid en viss total kostnad, ger den
bäst möjliga kvalitet av informationen
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* Smart upplagda mätningar
* Kostnadseffektiva procedurer för datainsamling
* Tillräckligt mycket data för att ge användbar information
* Systematiska observationsmetoder
Att observera fysisk belastning med hedern i behåll…
![Page 79: Ergonomisk risikovurdering · making the assessment. If a job consists of a variety of tasks, each task can be assessed separately.” David et al., 2008 Observer’s assessmentWorker’s](https://reader034.vdocuments.net/reader034/viewer/2022042214/5eb9e36c4ec52e2f832a7ad8/html5/thumbnails/79.jpg)
* Utspridda mätningar i tid
* Fler resurser på själva observationen, färre på underlaget
* Tillräckligt mycket data för att ge användbar information
Att observera fysisk belastning med hedern i behåll…
* Individer framför dagar framför mätningar inom dag
* Stillbilder framför filmsekvenser
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Shangri-La…
• Tydligare krav på ergonomisk dokumentation, som får ta tid
• Manualer för kvalitetssäkrad bedömning av belastningsdata
• Instrument för uppföljning av systematiskt arbetsmiljöarbete
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Referenser som förekommer i bilderna (1)
• Hansson G-Å, Arvidsson I, Ohlsson K, Nordander C, Mathiassen SE, Skerfving S, Balogh I:
Precision of measurements of physical workload during standardised manual handling. Part II:
Inclinometry of head, upper back, neck and upper arms. J Electromyogr Kinesiol 16 (2006): 125-136
• Liv P, Mathiassen SE, Svendsen SW: Theoretical and empirical efficiency of sampling strategies for
estimating upper arm elevation. Ann Occup Hyg 55 (2011): 436-449
• Mathiassen SE, Burdorf A, van der Beek AJ: Statistical power and measurement allocation in
ergonomic intervention studies assessing upper trapezius EMG amplitude. A case study of assembly
work. J Electromyogr Kinesiol 12 (2002): 27-39
• Mathiassen SE, Paquet V: The ability of limited exposure sampling to detect effects of interventions
that reduce the occurrence of pronounced trunk inclination. Appl Ergon 41 (2010): 295-304
• Mathiassen SE, Liv P, Wahlström J: Cost-efficient measurement strategies for posture observations
based on video recordings. Appl Ergon 44 (2013): 609-617
• Nordander C, Balogh I, Mathiassen SE, Ohlsson K, Unge J, Skerfving S, Hansson G-Å: Precision of
measurements of physical workload during standardised manual handling. Part I: Surface
electromyography of m. trapezius, m. infraspinatus and the forearm extensors. J Electromyogr
Kinesiol 14 (2004): 443-454
• Paquet V, Punnett L, Woskie S, Buchholz B: Reliable exposure assessment strategies for physical
ergonomics stressors in construction and other non-routinized work. Ergonomics 48 (2005): 1200-
1219
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Referenser som förekommer i bilderna (2)
• Rezagholi M, Mathiassen SE, Liv P: Cost efficiency comparison of four video-based techniques for
assessing upper arm postures. Ergonomics 55 (2012): 350-360
• Takala EP, Pehkonen I, Forsman M, Hansson G-Å, Mathiassen SE, Neumann WP, Sjøgaard G,
Veiersted KB, Westgaard RH, Winkel J: Systematic evaluation of observational methods assessing
biomechanical exposures at work. Scand J Work Environ Health 36 (2010): 3-24
• Trask C, Mathiassen SE, Wahlström J, Heiden M, Rezagholi M: Data collection costs in industrial
environments for three occupational posture exposure assessment methods. BMC Med Res
Methodol 12 (2012): 89
• Trask C, Mathiassen SE, Jackson JA, Wahlström J: Data processing costs for three posture
assessment methods. BMC Med Res Methodol 13 (2013): 124
• Trask C, Mathiassen SE, Wahlström J, Forsman M: Cost-efficient assessment of biomechanical
exposure in occupational groups, exemplified by posture observation and inclinometry. Scand J
Work Environ Health (2014; ePub ahead of print; doi: 10.5271/sjweh.3416)
• Wahlström J, Mathiassen SE, Liv P, Hedlund P, Forsman M, Ahlgren C: Upper arm postures and
movements in female hairdressers across four full working days. Ann Occup Hyg 54 (2010): 584-594
• Winkel J, Mathiassen SE: Assessment of physical work load in epidemiological studies - concepts,
issues and operational considerations. Ergonomics 37 (1994): 979-988
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Extra referenser
• Burdorf A, van der Beek AJ: Exposure assessment strategies for work-related risk factors for
musculoskeletal disorders. Scand J Work Environ Health 25 suppl 4 (1999): 25-30
• Denis D, Lortie M, Rossignol M: Observation procedures characterizing occupational physical
activities: critical review. Int J Occup Safety Ergon 6 (2000): 463-491
• Hoozemans MJM, Burdorf A, van der Beek AJ, Frings-Dresen MHW, Mathiassen SE: Group-based
measurement strategies in exposure assessment explored by bootstrapping. Scand J Work Environ
Health 27 (2001): 125-132
• Mathiassen SE, Burdorf A, van der Beek AJ, Hansson G-Å: Efficient one-day sampling of
mechanical job exposure data - a study based on upper trapezius activity in cleaners and office
workers. Am Ind Hyg Assoc J 64 (2003): 196-211
• Mathiassen SE, Wahlström J, Forsman M: Bias and imprecision in posture percentile variables
estimated from short exposure samples. BMC Med Res Methodol 12 (2012): 36
• Svendsen SW, Mathiassen SE, Bonde JP: Task-based exposure assessment in ergonomic
epidemiology - a study of upper arm elevation in the jobs of machinists, car mechanics, and house
painters. Occup Environ Med 62 (2005): 18-26
• Trask C, Teschke K, Morrison J, Johnson PW, Village J, Koehoorn M: How long is long enough?
Evaluating sampling durations for low back EMG assessment. J Occup Environ Hyg 5 (2008): 664-
670
• van der Beek AJ, Frings-Dresen MHW: Assessment of mechanical exposure in ergonomic
epidemiology. Occup Environ Med 55 (1998): 291-299
• Winkel J, Mathiassen SE: Assessment of physical work load in epidemiologic studies: concepts,
issues and operational considerations. Ergonomics 37 (1994): 979-988
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* För osmarta
* För dyra
* För begränsade
Observationer av fysisk belastning är ofta…
* För osystematiska
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Arbetsställningar ändrar sig över tid…
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s2BS s2
BD s2WD
Storleken av belastningsvariabilitet
Montering; median trapEMG (Mathiassen et al. 2002)
148 89 23
0.8 1.4 -
37 21 -
22 9 237
Montering; median trapEMG (Nordander et al. 2004)
Montering; median armelev (Hansson et al. 2006)
Bilmekaniker; medel armelev (Liv et al. 2011)
14 10 - Frisörer; median armelev (Wahlström et al. 2010)
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CVBS CVBD CVWD
Storleken av belastningsvariabilitet
Montering; median trapEMG (Mathiassen et al. 2002)
0,24 0,19 0,10
0,15 0,20 -
0,19 0,14 -
0,16 0,10 0,52
Montering; median trapEMG (Nordander et al. 2004)
Montering; median armelev (Hansson et al. 2006)
Bilmekaniker; medel armelev (Liv et al. 2011)
0,16 0,14 - Frisörer; median armelev (Wahlström et al. 2010)
CV: standardavvikelse/medelvärde
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Mer data ger bättre säkerhet
Paquet et al., 2005
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Mer data ger bättre säkerhet
Medel: 13,4
Hoozemans et al., 2001
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Mellan dagar inom individ
Inom dag inom individ
May
13
May
12
May
14
Mellan individer
Tre nivåer av variabilitet
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Variance components and unit costs
Time >90 Time <15
Variance components:
Between films s2WS 3.7 179.6
Between observers s2BO 0.0 87.0
Within observer s2WO 9.0 130.6
Unit costs:
Filming, € CF 36 36
Observation, € CO 7 7
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Bootstrapping
“När jag tittade ner såg jag att mina stövlar var försedda med
ovanligt långa och stadiga stroppar. Jag tog tag i dom med ett fast
grepp och drog av all min kraft. Snart hade jag dragit upp mig själv
till kanten och kunde träda ut på fasta marken utan vidare
bekymmer.”
Baron von Münchhausen:
Sällsamma resor och äventyr
till lands och vatten
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Variance between subject’s means
Variance of a subject’s mean
Variance components and
Number and allocation of measurements
varBS + varBD/nd+varWD/nd nq ( )/ns
Expected precision of a group mean:
I.e.: Number of subjects
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Investigated measurement strategies
• Budget up to 1000€
• 1, 2, 3, 4 observers
• 1, 2, 3, 4 observation repeats per observer
• Number of videos as allowed by budget
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Varianskomponenter
Antal mätningar
Biologisk varians, observatörsvarians,
antal mätningar:
Hur stor blir osäkerheten på resultatet?
s2µ = s2
WS/nd +
s2BO/no +
s2WO/ndnonr
Effektivitet (prestanda, information):
1/√s2µ
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Information
=
1/√s2WS/nd+s2
BO/no+s2WO/ndnonr
Varianskomponenter
Antal mätningar
Information:
1/SD
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Ctot = CF·nd +
CO·ndnonr
Kostnader för filmning och observation –
kostnadsfunktion
Enhetskostnader
Antal mätningar
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0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
0 200 400 600 800 1000
Cost and efficiency – Time >90°
1
3 2
5 4
10 9 8 7
6
12 14
16 18
20 22
# videos
Cost, €
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Effic
iency
Obs1Rep1
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0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
0 200 400 600 800 1000
Cost and efficiency – Time >90°
14
14 videos
9 videos
9
Cost, €
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Effic
iency
Obs1Rep4
Obs1Rep1
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0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
0 200 400 600 800 1000
Value for the money – Time >90°
Cost, €
Using 600 € on having 1 observer
look at 14 videos once
decreases efficiency by 15%
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Effic
iency
Obs1Rep1
Obs1Rep4
Obs2Rep1
Obs2Rep4
Obs4Rep1
Obs4Rep4
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0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
0 200 400 600 800 1000
Money for the value – Time >90°
Cost, €
Getting an efficiency of 1.0 by
having 1 observer look at 13 videos
once increases cost by 46%
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Effic
iency
Obs1Rep1
Obs1Rep4
Obs2Rep1
Obs2Rep4
Obs4Rep1
Obs4Rep4
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Value for the money – Time <15°
0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Cost, €
Using 600 € on having 1 observer
look at 14 videos once decreases
efficiency by 36%
0.20
0.15
0.10
0.05
0.00
Effic
iency
Obs1Rep1
Obs1Rep4
Obs2Rep1
Obs2Rep4
Obs4Rep1
Obs4Rep4
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Budget influences ranking – Time <15°
0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Cost, €
0.20
0.15
0.10
0.05
0.00
Effic
iency
Obs1Rep1
Obs1Rep4
Obs2Rep1
Obs2Rep4
Obs4Rep1
Obs4Rep4
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Money for the value – Time <15°
0,00
0,05
0,10
0,15
0,20
0 200 400 600 800 1000
Cost, €
0.20
0.15
0.10
0.05
0.00
Effic
iency
Getting an efficiency of 0.10 by
having 1 observer look at 23 videos
once increases cost by 415%
Obs1Rep1
Obs1Rep4
Obs2Rep1
Obs2Rep4
Obs4Rep1
Obs4Rep4
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Mätstrategier –
vad vill vi veta
• Hur mycket varierar belastning mellan
och inom individer i olika yrken
• Hur väl fungerar olika mätverktyg i olika yrken
• Hur mycket belastningsdata är nödvändigt för olika syften
• Hur lägger man bäst upp en mätstrategi i tid
• Hur väl kan man förutsäga prestandan av olika mätstrategier
• Vad kostar det att använda olika mätverktyg,
och hur mycket information får man för pengarna
• Går det att uppskatta ”dyra” belastningsdata
med ”billig” kunskap om personen eller arbetet