June 28 , 2002
Testing for Employers: A Means
of Reducing Injuries Caused
MED-TOX HEALTH SERVICES
The need for physical testing for
workers in manual materials handling jobs has been recognized
by occupational health professionals, risk managers, and ergonomists
increasingly over the past few years. Risk managers have
an interest in job safety and reducing workers' compensation
costs. Physicians and occupational health nurses seek to
reduce unnecessary injuries and find ways to better predict
in advance those most likely to become injured while ergonomists
seek to redesign jobs to better match the work to the worker.
Back Injuries: A Continuing
According to the National Academy
of Sciences (NAS, 2001) study on musculoskeletal disorders
and work, back injuries account for over one million workers
losing time from work each year. NAS conservatively estimates
that back injuries cost employers approximately $50 billion
dollars each year. According to this study, the most frequent
risk factor associated with back injuries was "lifting
and/or carrying loads." Other risk factors identified
included bending and twisting and whole body vibration. However,
no risk factor came close to the importance of lifting and
carrying loads. Injuries occur when there is a mismatch between
the worker and the work. Workers without sufficient strength
to perform their job tasks incur injuries of overexertion.
Reducing Injuries Caused by
Since overexertion injuries account
for a significant number of all work-related back injuries
to employees, it makes sense to reduce the probability of
their occurrence. Hiring workers with the adequate strength
to perform the job can reduce these injuries. One way to
determine if a potential employee has the ability to perform
the job is by administering a strength test. Approaches to
strength testing must meet two goals:
1. Include a valid and legally
defensible job analysis of the essential, frequently performed,
and physically demanding tasks associated with the occupation.
2. Ensure that the physical ability
test is job-related, valid, and reliable that can confidently
be used in the selection of individuals for physically demanding
Experience with the model described
below has resulted in the preplacement testing of more than
10,000 job applicants in California alone.
Strength tests must be chosen on
the basis of safety, reliability, and validity. Ability tests
are safer than job simulation tests because it is preferable
to determine how much weight an applicant can lift rather
than asking the applicant to lift a heavy weight. If the
applicant does not have the necessary strength to lift the
weight an injury may occur during the test.
Valid strength tests should not
be confused with Functional Capacity Evaluations (FCE). FCEs
typically involve multiple measurements of various physical
dimensions including some assessments of strength and flexibility.
Periodic measurements using the same FCE can document changes
in a patient's functional status over time. However, FCEs
typically suffer from the fact that they are basically measures
of function with little or no evidence linking them to successful
performance on a particular job. In a comprehensive review
of several widely used FCEs, Innes and Straker, (2000), found
that "most work-related assessments have limited evidence
of validity" and none had sufficient psychometric evidence
to support an employment screening decision. Because employers
have legal responsibilities to not discriminate against either
females or persons with disabilities, tests such as FCEs are
unacceptable choices for physically screening workers prior
to placement. Strength tests must be designed to ensure that
the ability test (selection device) is empirically demonstrated
to be related to the job.
ADA and Gender Discrimination
In a series of decisions over the
past three years, the US Supreme Court has narrowed the coverage
of the Americans with Disabilities Act to such a degree that
strength tests should rarely be subject to challenge. In
order to be subject to the provisions of the ADA, a job applicant
must be so disabled as to have difficulty performing activities
of daily living such as brushing one's teeth, walking, seeing,
and so forth. The disability can no longer be trivial: it
must be both serious and enduring. It will be difficult to
find job applicants so disabled that they have difficulty
dressing themselves, walking, and brushing their teeth yet
be capable of performing a physically demanding job for which
a strength test has been validated.
The primary concern for employers
assessing the strength abilities of new hires will be discrimination
on account of gender. Since adverse impact occurs on virtually
all tests of physical ability, the need to demonstrate job-relatedness
and validity will always be present. Job-relatedness and
validity are demonstrated by job analysis and the demonstration
of an empirical relationship between the test and performance
on the job.
To document job-relatedness, it
is necessary collect job information from experienced workers.
The job analysis inquiry is directed at collecting tasks from
incumbents which require static strength. Static strength
involves the continuous exertion of maximum muscle force for
a brief period time. Tasks that involve the lifting, pulling,
pushing, or carrying of objects and materials require static
strength. Following the collection of job information, the
work site should be visited to directly examine tools, equipment
and materials that had been described by workers during the
meeting. An industrial scale and/or a force gauge is used
to directly weigh as many of the relevant objects as possible.
If additional materials or tools are found that are also lifted,
these objects are weighed, the weights recorded, and the lifting
tasks added to a task listing produced for worker surveys.
In order to measure a job, one needs a measuring tool. Rating
scales are the most useful measuring tools when performing
job analysis activities with task inventories. Rating scales
can have a number of customized features depending on the
job and specific organizational needs. To validate a strength
test, however, it is important to illicit from workers:
1. Whether or not the task
2. How physically demanding is
3. How far the object is carried?
4. How often the task is performed?
5. How important the task is
to the job?
Typically, a sample of employees
complete a task inventory. Employee ratings on the various
dimensions are then statistically examined to determine the
most critical, frequently performed, and physically demanding
Work Sample Development
Having determined which strength
tasks are critical for the job, it is next necessary to determine
which tasks are suitable for utilization as work samples.
Ideally, the tasks selected should be among the most demanding
tasks workers are expected to perform. Additionally, other
criteria should be considered including:
Safety to incumbents. Tasks
selected should be safe to perform in a testing situation.
Some tasks might not be dangerous to experienced workers,
but could be to a novice.
Reasonable time to administer.
The tasks selected for work sample development should
be those which can be completed in a reasonable amount of
Unambiguous scoring and clarity
of results. Tasks selected should be amiable to an
unambiguous scoring or rating system. There should be no
disagreement as to what constituted various levels of performance.
Subjective ratings on "style of lifting" or "ease
of lifting" are less suitable when objective measures
tasks selected should be as simple as possible from both the
point of view of instruction to incumbents and administration
of the work sample.
Independence from training
and experience. The tasks selected should be dependent
upon strength and not "tricks of the trade" for
success. Novice and experienced individuals with the same
level of strength should have the same score.
tasks selected should be commonly performed by as many workers
Critical tasks that meet the criteria
can be categorized in a variety of ways. For example, all
tasks involving the use of a wheelbarrow or a dolly might
form a group or task category called wheelbarrow tasks. Alternatively,
all tasks that involve work at a particular work site, or
all tasks performed while repairing heavy equipment could
form other groups. The nature of the job and tasks performed
typically lend themselves to the selection of appropriate
task categories. Task categories are important because they
help organize the work and ensure that a variety of lifting
tasks can be used to construct work samples. An example
of five related tasks that form a category might be:
Five-Gallon Container (Paint, Joint Compound, Floor Sealer) Tasks
1. Lift/carry a five-gallon can of floor sealer (approx. weight 46.3 lbs.).
2. Carry a five-gallon bucket of paint (55.4 lbs.).
3. Lift/handle a five-gallon bucket of joint compound (51 lbs.).
4. Lift a five-gallon bucket of paint into the back of a vehicle (55.4 lbs.).
5. Lift a five-gallon bucket of paint up onto a stack of other five-gallon
paint buckets (55.4 lbs.).
Work samples may then be developed
from these categories of common critical tasks. For example,
a work sample for these tasks might be constructed as:
Five-Gallon Bucket Stack Work Sample
Approach a row of four five-gallon buckets of paint. Stack three
of the buckets on top of one of the bucket furthest to the
left. Next, take the top bucket off the stack and carry it
15 feet to a truck bed. Set it down and release grip. Re-grip
the bucket and return to the stack of buckets. Next, place
the bucket of paint beside the stack and replace the two remaining
cans on the ground in a row, as they were initially.
Such an event would be timed. Individuals
who struggle with this event will take longer than those who
can perform the task with ease.
Selecting Appropriate Static
Depending on the nature of the
ability being tested, a wide variety of tests are available.
For strength tests, we have used the Jackson Strength Evaluation
System (JSES) and found it to be a valid and reliable predictor
of the ability to perform lifting, pushing, pulling, and carrying
tasks. The JSES has several qualities that make it ideal
for employment testing. It has been shown to be safe and
practical. Results should be obtainable within 15 minutes.
The test is highly portable making it ideal for workplace
A sample of experienced workers
is typically chosen for test validation. The sample should
consist of individuals from various ages, racial groups and
both genders. Field testing consists of a brief medical screening,
informed consent, and an explanation of the tests. Participants
are first administered the Jackson Strength Evaluation System
which consists of four strength tests. Participants first
exert a constant force for three seconds on three tests which
use the lifting bar. These tests consist of the Arm Lift,
the Shoulder Lift and the Trunk Pull tests. The last test
consists of grip strength as measured by a hand dynamometer.
All four tests have an electronic monitor connected to each
load cell to record the peak and average amount of force exerted
in pounds of force. Next, the simulations are performed by
the participants. The simulations consist of actual work
samples of the job such as the Five-Gallon Bucket Stack described
above. Participants are given ample time to rest between events
and may decline testing at any time.
Participants are instructed not
to run or to perform the work at an unnatural pace. Participants
are asked to envision a day in which they had a lot of different
tasks to perform. When one task was completed, other important
tasks are to follow. Participants are instructed to work
at what might be considered a heavier than average pace, but
not one that was unrealistic or unrepresentative of the pace
at which they might work on a busy day. Scores are recorded.
Reliability of the JSES is assessed
by comparing the scores of the two recorded trials on each
test. Reliability typically ranges from a low of .97 to a
high of .99. Correlation coefficients are computed for all
tests and work samples to determine their interrelationships
and lack thereof. Multiple regression analysis is used to
derive equations to predict the performance of individuals
on the work sample test who have only taken the JSES. Evidence
for validity is assessed by statistical analysis to determine
how well each regression equation is predictive of work sample
performance. The validity coefficients obtained in the MED-TOX
studies strongly supports the use of the Jackson Strength
Evaluation System as a valid predictor of the ability to lift
and carry heavy loads.
Passing Levels (Cut-off scores)
Setting cut-off scores is a particularly
complex area of test construction. MED-TOX utilizes multiple
forms of evidence to arrive a cutoff level that is consistent
with business necessity. Cut-off scores should permit the
selection of qualified workers, be based on the results of
the job analysis, and account for the performance of currently
employed workers. The final cutoff permits the employment
of capable workers while screening out those persons who are
likely to be unable to perform or are highly likely to suffer
a disabling overexertion injury if placed on the job.
Strength testing job applicants
is the single most cost effective selection device an employer
can make to reduce workers' compensation and other injury-related
costs. The relationship between musculoskeletal injuries
and lack of strength has been repeatedly demonstrated. Stronger
and more fit workers are more productive and sustain far fewer
back injuries than weaker workers. Strength tests permit
the selection of individuals most likely to be able to perform
the tasks without undue risk of injury to themselves and to
screen-out persons who do not possess sufficient physical
ability to adequately perform the job.
National Academy of Sciences (2001).
Musculoskeletal Disorders in the Workplace. Washington,
DC: National Academy Press.
Innes, E. & Straker, L. (2000).
Commercially available work-related assessments: are they
reliable and valid? In. D. R. Worth (Ed), Moving in
on Occupational Injury. Boston: Butterworth-Heinemann,
Copyright © 2002 by WorkCare™
All Rights Reserved
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