We thanks Barratt and colleagues for their comments. We agree that
"care should be taken to validate model estimates with empirical
measurements wherever possible". Barratt and colleagues cite two stations
from the European Environment Agency database as located in the Railway
Ring and they report increasing NO2 concentrations from 2001 to 2005.
However, one station (IT0953A) is actually located i...
We thanks Barratt and colleagues for their comments. We agree that
"care should be taken to validate model estimates with empirical
measurements wherever possible". Barratt and colleagues cite two stations
from the European Environment Agency database as located in the Railway
Ring and they report increasing NO2 concentrations from 2001 to 2005.
However, one station (IT0953A) is actually located in the middle of a
large park within the Railway Ring, and thus reflecting urban background
concentrations, while the other station is not located in the Railway
Ring, making a direct validation nearly impossible. The correct code of
another traffic station located within the Railway Ring is IT0828A and the
annual mean NO2 concentration went from 80 ?g/m3 in 2001 to 68 ?g/m3 in
2005, which is a clear decrease supporting our work.
Moreover, official data from the Regional Environmental Agency
document that in Rome there was a decrease in nitrogen dioxide (NO2)
concentrations in most of the fixed monitoring stations from 2001 to
2005.[1] Moreover, Cattani et al. have documented a decrease in both NO2
and PM concentrations, especially in sites located near traffic, over a
longer period.[2]
That NOx emission standards of the different EURO vehicle classes are
much smaller than initially anticipated when the policy was formulated is
discovered very recently, and was not known at the time of this study.
Modelling studies are hampered by assumptions about for example emission
factors which may not be correct. Policy evaluation by measurements will
encounter difficulties as well, particularly by other developments
unrelated to the policy (for example an increase in the proportion of
diesel vehicles in the London congestion charging zone). Apart from
traffic other sources of air pollution on both the local and regional
scale, coupled with varying meteorological conditions could all confuse
air pollution trends. Therefore, multiple time windows surrounding the
policy and inclusion of sites not affected by the policy should be
evaluated in a proper empirical evaluation. Since this data was not
readily available at the time of this study, we performed a modelling
approach, reflecting real word conditions as close as possible.
2. Cattani G, Di Menno di Bucchianico A, Dina D, et al. Evaluation of
the temporal variation of air quality in Rome, Italy, from 1999 to 2008.
Ann Ist Super Sanita. 2010;46:242-53.
It is good to see some scientific rigour applied in this important
area. It is interesting to note however that there is no definition of
occupational dermatitis. It is a reportable and prescribed disease in the
UK, and can cause major impact on workers who suffer from it, but the
question is whether healthcare workers who have perhaps a period of dry
skin managed with ease, should be regarded has suffering from an
occu...
It is good to see some scientific rigour applied in this important
area. It is interesting to note however that there is no definition of
occupational dermatitis. It is a reportable and prescribed disease in the
UK, and can cause major impact on workers who suffer from it, but the
question is whether healthcare workers who have perhaps a period of dry
skin managed with ease, should be regarded has suffering from an
occupational disease. The answer to such a question is important to the
context of this paper and to the subject as a whole.
The title of the paper is on 'management' therefore relates to those who
have the condition, but there are of course in addition, major issues of
risk reduction and control, which must run in parallel. While the paper
makes mention of sensitisation in its background section, this important
group does not feature in the review.
In its later sections the term occupational dermatitis, is often reduced
just to 'dermatitis'. Does this mean that the recommendations apply
equally to workers with non occupational skin problems, such as psoriasis
or eczema, both in the pre-employment and in service situations?
Cesaroni et al make an assessment of the health benefits of a traffic management scheme in Rome based on changes in vehicle emissions and associated chronic risk factors(1). The authors estimate that a combination of the policy intervention and unrelated fleet changes caused a 38% reduction in the annual mean exposure of NO2 and a 29% reduction of PM10 within the 'railway ring' restricted zone bet...
Cesaroni et al make an assessment of the health benefits of a traffic management scheme in Rome based on changes in vehicle emissions and associated chronic risk factors(1). The authors estimate that a combination of the policy intervention and unrelated fleet changes caused a 38% reduction in the annual mean exposure of NO2 and a 29% reduction of PM10 within the 'railway ring' restricted zone between 2001 and 2005. The majority of this decrease was unrelated to the intervention, however, NO2 reductions specifically driven by the policy, were translated to 1387 years of life gained per 100,000 residents.
We strongly believe that such statements based solely on modelled and hence theoretical decreases in pollution require validation using empirical data. Measurements from the European Environment Agency's air quality database(2) show that measured annual mean NO2 concentrations within the 'railway ring' zone actually increased between 2001 and 2005 (80 ug/m3 to 82 ug/m3 at roadside site IT0946A and 39 ug/m3 to 41 ug/m3 at background site IT0953A). It is therefore evident that the assumptions used in the analysis did not reflect real world conditions.
Similarly, in studying the impacts of the London Congestion Charging Scheme, Kelly et al, found little evidence of a beneficial effect on monitored concentrations of NO2 and PM10, despite a large and sustained reduction in vehicle numbers(3). This was attributed to the relatively small area of the zone and an increase in the proportion of the vehicle fleet using diesel engines. It is also now widely accepted that the Euro emission standards are not delivering the predicted reductions in NOX(4).
While theoretical estimations of the health benefits of policy interventions are welcome, care should be taken to validate these estimates with empirical measurements wherever possible as man and machine rarely behave as predicted.
References:
1 Cesaroni G, Boogaard H, Jonkers S, Porta D, Badaloni C, Cattani G, Forastiere F, Hoek G. Health benefits of traffic-related air pollution reduction in different socioeconomic groups: the effect of low-emission zoning in Rome. Occup Environ Med. 2012;69(2):133-9.
3 Kelly F.J., Anderson H.R., Armstrong B., Atkinson R, Barratt B., Beevers S.D, Derwent D., Green D., Mudway I., Wilkinson P., 2011. The Impact of the Congestion Charging Scheme on Air Quality in London. Research Report Number 155. Health Effects Institute, Boston, MA, USA. April 2011. Available from http://pubs.healtheffects.org/types.php?type=1.
4 Carslaw D.C., Beevers S.D., Westmoreland E., Williams W., Tate J., Murrells T., Stedman J., Li Y., Grice S., Kent A., Tsagatakis I., 2011. Trends in NOX and NO2 emissions and ambient measurements in the UK. Report for Defra, March 2011. Available from http://uk-air.defra.gov.uk/library/reports?report_id=645.
High temperatures and mortality - even more relevant in desert
environments.
Your editorial on exposure to high ambient temperatures and mortality
is timely [1]. The Gasparrini et al.[2] paper on ambient air temperatures
and mortality in temperate England and Wales provides further support for
population-level preventive measures to reduce the likelihood of adverse
health effects from elev...
High temperatures and mortality - even more relevant in desert
environments.
Your editorial on exposure to high ambient temperatures and mortality
is timely [1]. The Gasparrini et al.[2] paper on ambient air temperatures
and mortality in temperate England and Wales provides further support for
population-level preventive measures to reduce the likelihood of adverse
health effects from elevated environmental temperatures.
The risk of heat-related illness and death is especially relevant to
desert environments, such as in the United Arab Emirates (UAE), where
summer temperatures can often exceed 50 degrees Celsius. In recent years,
the risk of morbidity and mortality from heat exposure was compounded when
the holy month of Ramadan coincided with summer in the Middle East. During
Ramadan, Muslims abstain from consuming fluids or food during daylight
hours. Additional risk factors for these workers are prolonged day shifts,
strenuous outdoor manual work and inadequate rest breaks. Muslim workers
constitute a majority of the expatriate workforce in several Middle
Eastern countries. Preventive measures to reduce the likelihood of
morbidity and/or mortality in this group are particularly pertinent over
the next few years when Ramadan will again fall during summer. In the UAE,
the Health Authority of Abu Dhabi developed a "Safety in the Heat"
campaign which distributed educational materials in five different
languages to over 800,000 outdoor workers focusing on self-monitoring
hydration status using urine colour, adequate hydration before and after
fasting, and self-pacing strategies whilst performing physical activity
[3]. An environmental early warning system could be developed using a
composite index of thermal stress incorporating several environmental
parameters (i.e. dry bulb temperature, wet bulb temperature, wind speed
and radiant heat). Another index is the Thermal Work Limit [4] which is a
good indicator of heat stress in outdoor workers and would be a useful
addendum to the Department of Health's Heatwave environmental monitoring
plan [5].
1. Ebi KL. High temperatures and cause-specific mortality. Occup
Environ Med 2012;69:3-4.
2. Gasparrini A, Armstrong B, Kovats S, Wilkinson P. The effect of
high temperatures on cause-specific mortality in England and Wales. Occup
Environ Med 2012;69:56-61.
3. Joubert D, Thomsen J, Harrison O. Safety in the Heat: A
Comprehensive Program for Prevention of Heat Illness Among Workers in Abu
Dhabi, United Arab Emirates, Am J Public Hlth 2011;101(3):395-398.
4. Brake DJ, Bates GP. Limiting metabolic rate (Thermal Work Limit)
as an Index of Thermal Stress. App Occup Environ Hyg 2002;17(3):176-186.
5. Department of Health. Heatwave: Plan for England - Protecting
Health and Reducing Harm From Extreme Heat and Heatwave. London:
Department of Health, 2009.
We thank Dr. Kawada for his interest in our manuscript entitled
"Associations of low-level urine cadmium with kidney function in lead
workers."[1] As discussed in the methods and shown in the footnotes to
Tables 3 and 4 in the manuscript, we adjusted for blood and tibia lead. We
have presented lead analyses in this cohort in multiple past
publications[2-8] so, in order to focus on the unique cadmium associations
and compl...
We thank Dr. Kawada for his interest in our manuscript entitled
"Associations of low-level urine cadmium with kidney function in lead
workers."[1] As discussed in the methods and shown in the footnotes to
Tables 3 and 4 in the manuscript, we adjusted for blood and tibia lead. We
have presented lead analyses in this cohort in multiple past
publications[2-8] so, in order to focus on the unique cadmium associations
and comply with space considerations, we did not show the lead regression
coefficients. Multiple linear regression was used in the analysis.
References:
1 Weaver VM, Kim NS, Jaar BG et al. Associations of low-level urine
cadmium with kidney function in lead workers. Occup Environ Med
2011;68:250-256. doi:oem.2010.056077 [pii]
10.1136/oem.2010.056077 [doi] [published Online First 2010/10/27].
2 Weaver VM, Lee BK, Ahn KD et al. Associations of lead biomarkers
with renal function in Korean lead workers. Occup Environ Med 2003;60:551-
62. 2003/07/29].
3 Weaver VM, Schwartz BS, Ahn KD et al. Associations of renal
function with polymorphisms in the delta-aminolevulinic acid dehydratase,
vitamin D receptor, and nitric oxide synthase genes in Korean lead
workers. Environ Health Perspect 2003;111:1613-9. 2003/10/07].
4 Weaver VM, Jaar BG, Schwartz BS et al. Associations among lead dose
biomarkers, uric acid, and renal function in Korean lead workers. Environ
Health Perspect 2005;113:36-42. 2005/01/01].
5 Weaver VM, Lee BK, Todd AC et al. Associations of patella lead and
other lead biomarkers with renal function in lead workers. J Occup Environ
Med 2005;47:235-43. doi:00043764-200503000-00005 [pii] [published Online
First 2005/03/12].
6 Weaver VM, Schwartz BS, Jaar BG et al. Associations of uric acid
with polymorphisms in the delta-aminolevulinic acid dehydratase, vitamin D
receptor, and nitric oxide synthase genes in Korean lead workers. Environ
Health Perspect 2005;113:1509-15. 2005/11/03].
7 Weaver VM, Lee BK, Todd AC et al. Effect modification by delta-
aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide
synthase gene polymorphisms on associations between patella lead and renal
function in lead workers. Environ Res 2006;102:61-9. doi:S0013-
9351(06)00002-8 [pii]
10.1016/j.envres.2006.01.001 [doi] [published Online First 2006/02/21].
8 Weaver VM, Griswold M, Todd AC et al. Longitudinal associations
between lead dose and renal function in lead workers. Environ Res
2009;109:101-7. doi:S0013-9351(08)00215-6 [pii]
10.1016/j.envres.2008.09.005 [doi] [published Online First 2008/11/29].
We appreciate the careful reading of our editorial [1] by Drs.
Mikkelsen and Andersen. We regret our omission of the one published NUDATA
study available at the time our editorial was submitted [2]. That study
reported significant associations between mouse usage time collected with
memory resident software and both, acute neck pain and acute shoulder
pain, among 2146 technical assistants. However, because i) median mouse...
We appreciate the careful reading of our editorial [1] by Drs.
Mikkelsen and Andersen. We regret our omission of the one published NUDATA
study available at the time our editorial was submitted [2]. That study
reported significant associations between mouse usage time collected with
memory resident software and both, acute neck pain and acute shoulder
pain, among 2146 technical assistants. However, because i) median mouse
usage time was 5.2 hours/week and median keyboard usage time was 0.9
hours/week, and ii) rates of moderate or greater musculoskeletal pain were
very low among the participating computer users, we are concerned about
the generalizability of the observed associations to workers with greater
mouse and keyboard use.
Regarding differences in associations with musculoskeletal disorders
(MSDs) observed across studies using self-reported estimates of computer
use versus memory resident software documentation of computer use, we made
no argument that one was correct and the other was incorrect. Rather, we
raised the concern that these two exposure assessment methods capture
different (but not totally unrelated) aspects of computer use relevant to
MSD risk. The absence of perfect correlation between self-reported
estimates of computer use and memory resident software documentation of
computer use may be due to error in self report, differences in the kind
of exposure information captured, or both. The claims of methodological
objectivity and validity presented by Mikkelsen and Andersen do not
address this fundamental question. We continue to believe, as noted in our
editorial, that a better understanding of the attributes of work captured
by self report and by computer registration software will clarify what
appear to be inconsistent results reported by studies using them.
1. Gerr F, Fethke N. Ascertaining computer use in studies of
musculoskeletal outcomes among computer workers: differences between self-
report and computer registration software. Occup Environ Med 2011; 68: 465
-66.
2. Andersen JH, Harhoff M, Grimstrup S, et al. Computer mouse use
predicts acute pain but not prolonged or chronic pain in the neck and
shoulder. Occup Environ Med 2008;65 :126-31.
In a recent editorial Gerr et al.[1] discuss computer work and
musculoskeletal outcomes based on self-reported exposure versus objective
recordings using computer software. They state that only one small study
(n=27) using objective recordings was published before a large study by
Ijmker et al.[2], published in the same issue as the editorial. They
failed to consider the results of two NUDATA papers based on more than
2...
In a recent editorial Gerr et al.[1] discuss computer work and
musculoskeletal outcomes based on self-reported exposure versus objective
recordings using computer software. They state that only one small study
(n=27) using objective recordings was published before a large study by
Ijmker et al.[2], published in the same issue as the editorial. They
failed to consider the results of two NUDATA papers based on more than
2000 study participants, one of them published in the OEM[3].
The results of the study of Ijmker et al. and the NUDATA studies
consistently indicate that sustained or severe pain outcomes were not
related to objective computer work recordings.
The editorial argues that the results of the study of Ijmker et al does
not invalidate the much larger literature in which self-reported computer
use was associated with musculoskeletal symptoms. The main argument seems
to be that objective recordings do not capture the relevant exposures,
e.g. holding the hands over the keyboard without keying and that different
cut points for such non-activity periods may invalidate the objective
recordings. However, objective software-based computer work recordings are
in very good accordance with other objective measures like video-
recordings, and much better than self-reported exposure. Furthermore,
within reasonable limits, different cut-off values for non-activity
periods do not change these relations or computer times very much. This is
consistent evidence from several studies and not from "preliminary
investigations", as stated in the editorial. Finally, exposure times based
on different cut off's are highly correlated, and their relation to
musculoskeletal outcomes will not vary much with different cut-offs [4].
Contrary to the editorial, we find it very unlikely that retrospective
self-reports about computer use during several months should capture
biologically important aspects of computer work which are not captured by
a validated objective method, which prospectively collects exact computer
use data on a daily basis.
References
1. Gerr F, Fethke N. Ascertaining computer use in studies of
musculoskeletal outcomes among computer workers: differences between self-
report and computer registration software. Occup Environ Med 2011; 68: 465
-66
2. IJmker S, Huysmans MA, van der Beek AJ, et al. Software-recorded
and self-reported duration of computer use in relation to the onset of
severe arm-wrist-hand pain and neck-shoulder pain.
Occup Environ Med 2011; 68: 502-9
3. Andersen JH, Harhoff M, Grimstrup S, et al. Computer mouse use
predicts acute pain but not prolonged or chronic pain in the neck and
shoulder. Occup Environ Med 2008;65 :126-31.
4. Mikkelsen S, Lassen CF, Vilstrup I, et al. Does computer use
affect the incidence of distal arm
pain? A one-year prospective study using objective measures of computer
use. Int Arch Occup Environ Health 2011 May 24 [Epub ahead of print]
We thank Dr. Mikkelsen and colleagues for their constructive comments
on our paper. Our responses to their three major questions are listed
below.
1) Why did we present various formulations of job strain?
The five formulations of job strain have been commonly reported in
the literature. Often, authors chose one or two formulations and thus
would not know if their results were consistent across differe...
We thank Dr. Mikkelsen and colleagues for their constructive comments
on our paper. Our responses to their three major questions are listed
below.
1) Why did we present various formulations of job strain?
The five formulations of job strain have been commonly reported in
the literature. Often, authors chose one or two formulations and thus
would not know if their results were consistent across different
formulations. In our study, with the encouragement of an OEM peer
reviewer, we presented results for all five formulations so that readers
can compare the results both across different formulations and with
previous job strain studies. We agree with Mikkelsen et al. that four of
the five formulations of job strain we examined could be the result of the
effect of job control only. As shown in Table 3, job demands was not
significantly associated with IMT whereas job control was.
2) Why did we not show the main effect coefficients for job demands
and control as we showed the coefficient for the multiplicative term in
Table 4?
When a multiplicative term is included in a regression model, the
main effects of the interacted variables have a more complex
interpretation;1 that is, the coefficients represent the magnitude of
effect for each variable when the other is 0. We showed the main effects
of the two variables in Table 3, which represent the magnitude of each
variable's effect when the other is controlled for. For the sake of
brevity, we did not show the coefficients for demands and control after
the multiplicative term was included in the model. This was explained in
the footnote for Table 4.
3) Why did we illustrate the interaction in dichotomous terms (Figure
1) and ignored that high job demands were protective?
Figure 1 is an illustration of the interaction, which could have been
constructed using the mean+1SD as "high" and the mean-1SD as "low" or
other ways. We used the median split again for the sake of simplicity and
also because it is a commonly used approach in the job strain literature.
We do recognize that the demand-control model was only partially supported
in our study; that is, job control was protective only for those who
reported high job demands. Overall, job demands did not have a
significant association with IMT, as shown in Table 3. The following
paragraph is our discussion on this finding from an earlier draft.
Unfortunately, this paragraph was excluded from the final version because
of the word limit.
Contrary to the demand-control model's prediction,2 we did not find
significant associations between IMT and job demands. The Cardiovascular
Risk in Young Finns Study also failed to find the same significant
association.3 The majority of CVD studies have found positive
associations between job demands and CVD,4 but Belki? et al.4 identified
five studies that reported an inverse association between psychological
job demands and CVD.5-9 In the MESA cohort, of which about 30% were
immigrants, the job demands scale had acceptable scale reliability among
U.S.-born participants but not among immigrants (Cronbach's alpha = 0.75
for U.S.-born, ranged from 0.45 to 0.65 for immigrants, depending on the
language used in data collection10). Limitations in the measure of job
demands used in heterogeneous samples like ours may have limited our
ability to detect associations of job demands with IMT.
References:
1. Cohen J, Cohen P. Applied Multiple Regression: Correlation
Analysis for the Behavioral Sciences. 2nd ed. Hillsdale, NJ: Lawrence
Erlbaum, 1983.
2. Karasek RA. Job demands, job decision latitude, and mental strain:
Implications for job redesign. Administrative Science Quarterly
1979;24:285-308.
3. Hinsta T, Kivim?ki M, Elovainio M, Vahtera J, Hintsanen M, Viikari
JSA, et al. Is the association between job strain and carotid intima-media
thickness attributable to pre-employment environmental and dispositional
factors? The Cardiovascular Risk in Young Finns Study. Occupational and
Environmental Medicine 2008;65:676-82.
4. Belki? KL, Landsbergis PA, Schnall P, Baker D. Is job strain a
major source of cardiovascular disease risk? Scand. J. Work Environ.
Health 2004;30(2):81-128.
5. Alterman T, Shekelle RB, Vernon SW, Burau KD. Decision latitude,
psychologic demand, job strain and coronary heart disease in the Western
Electric Study. American Journal of Epidemiology 1994;139:620-27.
6. Bobak M, Hertzman C, Skovoda Z, Marmot MG. Association between
psychosocial factors at work and non-fatal myocardial infarction in a
population based case-control study in Czech men. Epidemiology 1998;9:43-
47.
7. Hall EM, Johnson JV, Tsou TS. Women, occupation, and risk of
cardiovascular morbidity and mortality. Occupational Medicine 1993;8:709-
19.
8. Johnson JV, Stewart W, Hall EM, Fredlund P, Theorell T. Long-term
psychosocial work environment and cardiovascular mortality among Swedish
men. American Journal of Public Health 1996;86:324-31.
9. Steenland K, Johnson JV, Nowlin S. A follow-up study of job strain
and heart disease among males in the NHANES1 population. American Journal
of Industrial Medicine 1997;31:256-59.
10. Fujishiro K, Landsbergis P, Diez Roux AV, Hinckley Stukovsky K,
Shrager S, Baron S. Factorial invariance, scale reliability, and validity
of the decision latitude and psychological demands scales for immigrant
workers: The Multi-Ethnic Study of Atherosclerosis (MESA). Journal of
Immigrant and Minority Health 2010;13:533-40.
Self-report of duration of computer use is usually overestimated. The
search for a valid measure of exposure to keyboard/mouse use resulted in
the development of a computer registration software. The use of this new
software generated unexpected results when IJmker et al.1 found software-
recorded computer use was not significantly associated with upper
extremity/neck symptom onset while self-reported computer use was
sig...
Self-report of duration of computer use is usually overestimated. The
search for a valid measure of exposure to keyboard/mouse use resulted in
the development of a computer registration software. The use of this new
software generated unexpected results when IJmker et al.1 found software-
recorded computer use was not significantly associated with upper
extremity/neck symptom onset while self-reported computer use was
signficantly associated with symptoms in the neck/shoulder and arm/hand.
What is captured in the self-report that is missing in the software-
recorded duration of computer use? In the editorial by Gerr and Fethke2
reference is made to work by Homan and Armstrong3 that noted the potential
negative effect of time spent with hands held over the keyboard but
without keying. In our Medical-Ergonomic Program4 we refer to this
position as the 'action ready' posture when the forearm(s) is in full
pronation over the keyboard or mouse causing muscle activation of the
forearm extensor muscles. This may lead to the development of painful
trigger points in the forearm extensor muscles, a common area of
complaints by computer users.4 Activities such as reading, talking,
thinking etc. while using the computer are frequently accompanied by this
'action ready' posture. Time spent in these activities is included when
self-reporting duration of computer use but would not be captured in
computer registration software.
Other posture issues without keystrokes or mouse clicks involve the
neck/shoulder area. Computer users have a habit of not sitting up
straight against the back of the chair and carry their shoulders forward.
This posture activates the muscles involved with scapulae stabilization
and shortens the pectoralis minor4 resulting in painful trigger points in
the overused muscles . Neck/shoulder muscles are also activated when mouse
use is with the arm extended away from the body, when the monitor is too
far away and the chin juts forward or when the keyboard is too high and
the shoulders remain hiked to compensate. Maintenance of these postures
with or without keystrokes and mouse clicks are an etiology for upper
extremity symptoms that needs to be added to the exposure equation for
computer use.
1. IJmker S, Huysmans MA, van der Beek AJ, et al. Software-recorder
and self-reported duration of computer use in relation to the onset of
severe arm-wrist-hand pain and neck-shoulder pain. Occup Environ Med
2011;68:502-209.
2. Gerr F and Fethke N. Ascertaining computer use in studies of
musculoskeletal outcomes among computer workers: differences between self-
report and computer registration software. Occup Environ Med 2011;68:465-
466.
3. Homan MM and Armstrong TJ. Evaluation of three methodologies for
assessing work activity during computer use. AIHA J (Fairfax, VA)
2003;64:48-55.
4. Bleecker ML, Celio MA, Barnes SK. A medical-ergonomic program for
symptomatic keyboard/mouse users. JOEM 2011;53:561-567.
Fujishiro et al.1 recently published data on the association of job
demands and control with carotid artery intima-media thickness (IMT). The
joined effect of demands and control (strain) was analyzed by five
different strain definitions:
1. a quadrant term (median splits of demands and control),
2. combinations of tertiles of demands and control,
3. an additive term (demands minus control) ,
4. a quotient term (the ra...
Fujishiro et al.1 recently published data on the association of job
demands and control with carotid artery intima-media thickness (IMT). The
joined effect of demands and control (strain) was analyzed by five
different strain definitions:
1. a quadrant term (median splits of demands and control),
2. combinations of tertiles of demands and control,
3. an additive term (demands minus control) ,
4. a quotient term (the ratio) and
5. a multiplicative term (the product).
The first three terms are linear combinations of demands and control,
which are less informative than the corresponding linear combination based
on regression analyses of the mutually adjusted effects of demands and
control. The quotient term implies interaction between demands and control
but does not examine if there is one, its size, form or statistical
significance. An effect of any of the first four strain terms may be due
to an effect of only one of the two factors. Why introduce a strain
measure of the joined effect of demands and control, if it may only
reflect the effect of one of these variables?
A parsimonious and informative way to examine the joined effect of demands
and control is regression analyses with demands, control and their
multiplicative term included as covariates. The authors published the
effects of the multiplicative term but not the main effects. These are
needed to evaluate the form of any interaction. The authors only
illustrate the form of the interaction by dichotomous combinations of
demands and control.
The authors interpret the interaction as confirmation of the job strain
theory because high job control protected against thick IMT, especially
among persons with high job demands. However, they overlook that high job
demands also protected against thick IMT. The interaction effect as a
whole was not in accordance with the job strain model.
References
1. Fujishiro K, Diez Roux AV, Landsbergis P, et al. Associations of
occupation, job control and job demands with intima-media thickness: The
Multi-Ethnic Study of Atherosclerosis (MESA). Occup Environ Med
2011;68:319-326.
Dear Editor,
We thanks Barratt and colleagues for their comments. We agree that "care should be taken to validate model estimates with empirical measurements wherever possible". Barratt and colleagues cite two stations from the European Environment Agency database as located in the Railway Ring and they report increasing NO2 concentrations from 2001 to 2005. However, one station (IT0953A) is actually located i...
It is good to see some scientific rigour applied in this important area. It is interesting to note however that there is no definition of occupational dermatitis. It is a reportable and prescribed disease in the UK, and can cause major impact on workers who suffer from it, but the question is whether healthcare workers who have perhaps a period of dry skin managed with ease, should be regarded has suffering from an occu...
Cesaroni et al make an assessment of the health benefits of a traffic management scheme in Rome based on changes in vehicle emissions and associated chronic risk factors(1). The authors estimate that a combination of the policy intervention and unrelated fleet changes caused a 38% reduction in the annual mean exposure of NO2 and a 29% reduction of PM10 within the 'railway ring' restricted zone bet...
Dear Editor,
High temperatures and mortality - even more relevant in desert environments.
Your editorial on exposure to high ambient temperatures and mortality is timely [1]. The Gasparrini et al.[2] paper on ambient air temperatures and mortality in temperate England and Wales provides further support for population-level preventive measures to reduce the likelihood of adverse health effects from elev...
We thank Dr. Kawada for his interest in our manuscript entitled "Associations of low-level urine cadmium with kidney function in lead workers."[1] As discussed in the methods and shown in the footnotes to Tables 3 and 4 in the manuscript, we adjusted for blood and tibia lead. We have presented lead analyses in this cohort in multiple past publications[2-8] so, in order to focus on the unique cadmium associations and compl...
We appreciate the careful reading of our editorial [1] by Drs. Mikkelsen and Andersen. We regret our omission of the one published NUDATA study available at the time our editorial was submitted [2]. That study reported significant associations between mouse usage time collected with memory resident software and both, acute neck pain and acute shoulder pain, among 2146 technical assistants. However, because i) median mouse...
In a recent editorial Gerr et al.[1] discuss computer work and musculoskeletal outcomes based on self-reported exposure versus objective recordings using computer software. They state that only one small study (n=27) using objective recordings was published before a large study by Ijmker et al.[2], published in the same issue as the editorial. They failed to consider the results of two NUDATA papers based on more than 2...
We thank Dr. Mikkelsen and colleagues for their constructive comments on our paper. Our responses to their three major questions are listed below.
1) Why did we present various formulations of job strain?
The five formulations of job strain have been commonly reported in the literature. Often, authors chose one or two formulations and thus would not know if their results were consistent across differe...
Self-report of duration of computer use is usually overestimated. The search for a valid measure of exposure to keyboard/mouse use resulted in the development of a computer registration software. The use of this new software generated unexpected results when IJmker et al.1 found software- recorded computer use was not significantly associated with upper extremity/neck symptom onset while self-reported computer use was sig...
Fujishiro et al.1 recently published data on the association of job demands and control with carotid artery intima-media thickness (IMT). The joined effect of demands and control (strain) was analyzed by five different strain definitions: 1. a quadrant term (median splits of demands and control), 2. combinations of tertiles of demands and control, 3. an additive term (demands minus control) , 4. a quotient term (the ra...
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