1. Psy 552 Ergonomics & Biomechanics
Lecture 17

2. 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.

3. 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. 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.

5. 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.

6. Method-Time Measurement (MTM)
MTM is a time estimation based upon elemental movements: …

7. MTM (cont)
Focuses on how:
... …
Uses TMUs…

8. Time & motion & ergonomics
These early studies created a foundation for ergonomic evaluations.
T&M studies do not generalize to ergonomics & biomechanics because they: …

9. Contemporary classification methods
Modern systems fall into two categories:
Passive
Active

10. Passive surveillance
Involves reviewing and analyzing pre-existing records such as: …

11. The passive process
Must be contrasted with results of other assessment techniques including: …

12. The passive process (cont)
Works best when records are computerized.
Should be conducted monthly if not quarterly.
Should contain requisite information: …

13. Indices Incident rate Point prevalence Severity index
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)

14. Passive advantages Low cost Makes use of available data
Historical perspective
Can be used to compare departments
Can be used to evaluate ergonomic interventions

15. 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

16. 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.

17. Active surveillance There are two types: Advantages Self-report Audits…

18. Active surveillance (cont)
Success depends on:
Short response times
Adequate response rates
Trained personnel
Employee memory
Tolerance of false positives

19. Active self-report tool features1. 2. 3. 4. 5. 6. 7. 8. 9.

20. Demographic & medical & work history

21. Analyzing WMSD data WMSD Yes No Total Risk Factor Present 10 30 40 476 80 14
106
120

22. 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.

24. 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.

25. Risk factors (cont) Posture targeting
Ovac Working Posture Analysis System
EMG

26. Risk factor surveillance: Disadvantages
They are more descriptive than evaluative.
A risk factor absent an injury requires evaluator judgment.
There are often few comparisons.

27. 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.