Psy 552 Ergonomics & BiomechanicsLecture 17
Work classification methodsThe 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 namesFrederick Taylor father of timemotion studies.Used time analysis of work to enhance productivity.Devised the four principles of scientific management
4 PrinciplesStudy 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 GilbrethStudied 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 & ergonomicsThese early studies created a foundation for ergonomic evaluations.T&M studies do not generalize to ergonomics & biomechanics because they:
Contemporary classification methodsModern systems fall into two categories:PassiveActive
Passive surveillanceInvolves reviewing and analyzing pre-existing records such as:
The passive processMust 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:
IndicesIncident rateIR = (# of illnesses x 200,000)/hours workedPoint prevalencePR = (# new + # old case at a given time)/number of workers at the same timeSeverity indexSI = (Total # lost work days due to the disorder(s))/(Total number of workers or hours worked in a period)
Passive advantagesLow costMakes use of available dataHistorical perspectiveCan be used to compare departmentsCan be used to evaluate ergonomic interventions
Passive disadvantagesThere are few accepted signs for WMSD.The true causes of WMSD are not well known.Putative factors are present in every job.These factors dont discriminate or differentiate jobs with and without histories of WMSD.Underreporting
Passive disadvantages (cont)Inconsistent record collectionWMSD occur over time and might not be reflected in records.Unknown reporting thresholdsRecords often fail to record the specific task being performed.
Active surveillanceThere are two types:Self-reportAuditsAdvantages
Active surveillance (cont)Success depends on:Short response timesAdequate response ratesTrained personnelEmployee memoryTolerance of false positives
Active self-report tool features220.127.116.11.18.104.22.168.9.
Demographic & medical & work history
Analyzing WMSD data
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.PrioritizeJobs with the highest incident rates.Jobs with the most effected people.Jobs where large changes have taken place.
Active surveillance: Risk factorsUsed by trained ergonomistProvide data based on educated observationsDo not require preexisting symptomsCan be used to evaluate work or equipment changes.Highly correlated with discomfort surveys.
Risk factors (cont)Posture targetingOvac Working Posture Analysis SystemEMG
Risk factor surveillance: DisadvantagesThey are more descriptive than evaluative.A risk factor absent an injury requires evaluator judgment.There are often few comparisons.
When conducting evaluationsCleary state your objectives.Understand sponsors 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.