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.