Study Questions

1

The findings and conclusions in this presentation are those of the authors and do not necessarily represent the views of the National

Institute for Occupational Safety and Health.

22

Can HCP quality be judged by evaluating their component parts?

Can historical data be useful in conducting such evaluations?

33

Historic review of 3 plants› 2 automotive plants

› 1 food processor

Covers period from 1970 through 1999

44

Historic noise exposure surveys

Historic audiometric test records

Employee work histories

Survey & focus group information on history of hearing conservation programs

55

Assigned by Job Title

› Used task-based noise surveys from 1990’s

› Multiple stage extrapolation to earlier jobs and job titles

66

Merged historical audiometric testing data with work histories (job titles)

Excellent match for food processor

Poor match for two automotive plants› More than half of all audiometric testing

conducted prior to initial work history

› Possibly due to migration of workers from other plants

77

History based on worker focus groups

Four historical HCP components created› % use of hearing protective devices (HPD)

› Audiometric testing frequency (calculated*)

› Frequency & responsiveness of noise monitoring

› Worker education (at shop meetings & testing)

99

Leq – cumulative measure of equivalent noise energy› 3 dB increase in TWA doubles exposure

› Does not accommodate uncertainty

› Historical estimates of duration better than intensity

Test alternative measure › Duration of exposure within 5 dB strata

› Weightings determined by the data

1010

Not addressing “hearing” per se› No need to define a threshold shift› No censorship of data

Use a sensitive yet robust measure› Use most sensitive frequencies› Incorporate bilateral measures› Average across multiple thresholds

Solution › Average at 3, 4 & 6 kHz across both ears

1111

Reduced data vs. data uncertainty› Do missing work histories = migration

between plants?

› Guessing could introduce large errors – considered too risk

Conclusion: Exclude audiograms with missing work histories

1212

Used dichotomous variables for all component quality measures› Used “better” vs. “worse” categorization

› Fortunately these varied by time and plant

› Did not necessarily improve over time

› The four components did not necessarily vary together

1414

1515

1616

Time from Baseline (1st valid) Audiogram

Reasons:› Better captures cumulative exposure

› Less dependent on accuracy of time cut-points for HCP quality measures

› Less dependent on latency of impact

1717

Variables included:› Intercept + dummy variables for plant

› Baseline (time=0) hearing threshold average

› Age at time of test (time=t)

› Leq + Duration of employment

Results› Duration of employment better predictor of

NIHL

› Majority of noise exposures between 85-95 dB

1818

Tested stratified model: duration of exposure within 5 dB TWA groups

duration at >=95 dB

duration at <95 dB

Baseline test 1 ….…test 2 …….test 3 ….. test n

Stratified duration for nth audiometric test period for this subject

Only strata significantly different from total exposure duration was for >=95 dB

1919

Model: duration of exposure by TWA and duration groups (over ‘x’ years in red)

duration at 95+ dB

duration at <95 dB


Two-way stratified duration for nth audiometric test period for this subject

Observed change in the dose-response relationship after 6 years

2020

HCP quality term entered separately for each component

Duration in “Worse” quality HCP (red) does not add to term

Duration in “Better” quality HCP


Duration in “Better” quality HCP for nth audiometric test period for this subject

Interaction terms yielded incoherent results

2121

2222

Base Model HPD Model Variables Coeff Coeff Intercept -1.89**** -2.18**** Plant X -1.02**** 0.62** Plant Y -0.39* -0.03

Reflecting Individual Characteristics Baseline Threshold -0.03**** -0.03**** Age at Test 0.08**** 0.08****

Reflecting NIHL Duration at <95dB / <=6 (years) 0.60**** 0.77**** Duration at >=95dB / <=6 (years) 0.82**** 1.04****

Duration at <95dB / >6 (years) 0.52**** 0.79**** Duration at >=95dB / >6 (years) 0.44*** 0.69****

Better HPD Use (Years) ----- -0.31****

Coefficients directly reflect average threshold change per variable unit

* p<0.05 **p<0.01 ***p<0.001 ****p<0.0001

2323

HPD programs effective in reducing NIHL› Reported enforcement of HPD policies

› Did not use information on types of devices No consensus on relative effectiveness of

different devices Dependent on use and acceptance of the

various devices

2424

Base Model HPD Model Variables Coeff Coeff Intercept -1.89**** -2.18**** Plant X -1.02**** 0.85**** Plant Y -0.39* -0.43*



Duration at <95dB / >6 (years) 0.52**** 0.44**** Duration at >=95dB / >6 (years) 0.44*** 0.31*

Better Audiometric Monitoring (Years) ----- 0.13***


* p<0.05 **p<0.01 ***p<0.001 ****p<0.0001

2525

Apparent reverse association (more testing, more threshold change detected)› Used mean time between tests

Need better descriptors

› Possibly due to artifacts People with poor hearing may resist initial testing Longer term employees & supervisors may resist

testing

2626

Base Model HPD Model Variables Coeff Coeff Intercept -1.89**** -2.09**** Plant X -1.02**** 0.48* Plant Y -0.39* -0.31



Duration at <95dB / >6 (years) 0.52**** 0.53**** Duration at >=95dB / >6 (years) 0.44**** 0.43***

Better Noise Monitoring (Years) ----- -0.13****


* p<0.05 **p<0.01 ***p<0.001 ****p<0.0001

2727

Apparent effect - BUT› Noise Exposure coefficients basically same

› Larger change in plant coefficient No variation by time within plants Only one plant had a “better program”

› Conclusion: Effect due to confounding

2828

Base Model HPD Model Variables Coeff Coeff Intercept -1.89**** -1.87**** Plant X -1.02**** -0.99**** Plant Y -0.39* -0.47**



Duration at <95dB / >6 (years) 0.52**** 0.54**** Duration at >=95dB / >6 (years) 0.44*** 0.43***

Better Worker Training (Years) ----- -0.04


* p<0.05 **p<0.01 ***p<0.001 ****p<0.0001

2929

Weak non-significant association› None of the programs were very

satisfactory Sporadic at best “Better” could only be used as a relative

term

› Conclusion: not enough variability

3030

3131

Were able to obtain interpretable results› Achieved some detail in modeling noise

› Effect of HPD use clearly demonstrated

However, limitations included:› Lack of variation

No quality programs for some components Sometimes no variation in time within plants

› Lack of good measures Need more details in quality and time frame

3232

Leq may not be suitable for historic studies› Too dependent on accuracy of TWA

Stratified duration shows possibilities› Explained much more NIHL

› Shape of dose response could be explored

› Useful for other time dependent variables E.g. Quality components

3333

More recent HCPs should have› Better and more detailed records

› More variation with good quality programs

Able to study more components

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Study Questions