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Psy 552 Ergonomics & BiomechanicsLecture 17
Work classification methods The need to address productivity, comfort and safety
dictate the need evaluate work methods.
In the quest to find the optimal method, early methods focused on productivity.
These work analysis methods have significant drawbacks that limit their use in ergonomics and biomechanics.
Historic names Frederick Taylor – father of time–motion
studies. Used time analysis of work to enhance
productivity. Devised the four principles of
scientific management
4 Principles Study work methods specifically. Select the best workers for the task and train
them. Develop cooperation between employees and
managers. Divide work according to ability, between
workers and managers depending upon who was best suited to perform it.
Frank and Lillian Gilbreth Studied work methods Capitalized on motion studies using
illuminated markers. Categorized motions in to “elemental
motions” that now serve as the basis for contemporary time and motion studies.
Method-Time Measurement (MTM) MTM is a time estimation based upon
elemental movements: …
MTM (cont) Focuses on how:
... … … …
Uses TMUs…
Time & motion & ergonomics These early studies created a foundation for
ergonomic evaluations. T&M studies do not generalize to ergonomics
& biomechanics because they: … … …
Contemporary classification methods Modern systems fall into two categories:
Passive Active
Passive surveillance Involves reviewing and analyzing pre-existing
records such as: …
The passive process Must be contrasted with results of other
assessment techniques including: … … …
The passive process (cont) Works best when records are computerized. Should be conducted monthly if not quarterly. Should contain requisite information:
… … … … …
Indices Incident rate
IR = (# of illnesses x 200,000)/hours worked Point prevalence
PR = (# new + # old case at a given time)/number of workers at the same time
Severity index SI = (Total # lost work days due to the
disorder(s))/(Total number of workers or hours worked in a period)
Passive advantages Low cost Makes use of available data Historical perspective Can be used to compare departments Can be used to evaluate ergonomic
interventions
Passive disadvantages There are few accepted “signs” for WMSD. The “true” causes of WMSD are not well
known. Putative factors are present in every job.
These factors don’t discriminate or differentiate jobs with and without histories of WMSD.
Underreporting
Passive disadvantages (cont) Inconsistent record collection WMSD occur over time and might not be
reflected in records. Unknown reporting thresholds Records often fail to record the specific task
being performed.
Active surveillance There are two types:
Self-report Audits
Advantages … … … …
Active surveillance (cont) Success depends on:
Short response times Adequate response rates Trained personnel Employee memory Tolerance of false positives
Active self-report tool features1.
2.
3.
4.
5.
6.
7.
8.
9.
Demographic & medical & work history
Analyzing WMSD data
WMSD
Yes No Total
Risk Factor Present
Yes 10 30 40
No 4 76 80
Total 14 106 120
Analyzing WMSD data (cont) WMSD incident rates > 1 per 200,000 should be
investigated further. In Washington State between 1988 and 1991 the
WMSD incident rate was .82 per 200,000 work hours.
Prioritize Jobs with the highest incident rates. Jobs with the most effected people. Jobs where large changes have taken place.
Active surveillance: Risk factors Used by trained ergonomist Provide data based on educated observations Do not require preexisting symptoms Can be used to evaluate work or equipment
changes. Highly correlated with discomfort surveys.
Risk factors (cont) Posture targeting Ovac Working Posture Analysis System EMG
Risk factor surveillance: Disadvantages They are more descriptive than evaluative. A risk factor absent an injury requires
evaluator judgment. There are often few comparisons.
When conducting evaluations Cleary state your objectives. Understand sponsor’s desires. Understand that you will not be universally
accepted. Select methods using an iterative process to
promote validity. Seek most recent scientific literature. Seek advice of experienced colleagues.