Final pres. work sampling (3)
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  • 2. INTRODUCTIONINTRODUCTION L. H. C. Tippet of British Cotton industryL. H. C. Tippet of British Cotton industry Also known as:Also known as: • Activity samplingActivity sampling • Ratio delay studyRatio delay study • Random observation methodRandom observation method • Snap reading methodSnap reading method • Observation ratio studyObservation ratio study
  • 3. BASIC CONCEPTSBASIC CONCEPTS & DEFINATION& DEFINATION Work sampling is a methodology for findingWork sampling is a methodology for finding the percentage occurrence of a certainthe percentage occurrence of a certain activity by statistical sampling & randomactivity by statistical sampling & random observations.observations.
  • 4. PROBABLITY DISTRIBUTIONPROBABLITY DISTRIBUTION • Probability based on the binomialProbability based on the binomial distributiondistribution (p + q)(p + q)nn = 1= 1 • Mean =Mean = npnp, Variance =, Variance = npqnpq • As n becomes large, the binomialAs n becomes large, the binomial distribution approaches the normaldistribution approaches the normal distributiondistribution • This proportion has distribution of Mean =This proportion has distribution of Mean = pp, Variance =, Variance = pq/npq/n
  • 5. STEPS OF WORKSTEPS OF WORK SAMPLINGSAMPLING 1.1. Define job activitiesDefine job activities 2.2. Determine number of observations inDetermine number of observations in work samplework sample nn == pp(1 -(1 - pp)) zz ee 22 wherewhere nn == sample size (number of samplesample size (number of sample observations)observations) zz == number of standard deviations from meannumber of standard deviations from mean for desired level of confidencefor desired level of confidence ee == degree of allowable error in sampledegree of allowable error in sample estimateestimate pp == proportion of time spent on a work activityproportion of time spent on a work activity
  • 6. Example of Sample SizeExample of Sample Size CalculationCalculation • Formula for calculation purposes simplifiesFormula for calculation purposes simplifies to: n = Zto: n = Z22 (1-P)(P)/(L(1-P)(P)/(L22 )) A work sampling study requires 95-percent confidence with five-percent accuracy. How many observations are required if the machine down time is eight percent? n = (1.960)2*(1-0.08)*0.08/(0.05)2 n = 225,76 observations
  • 7. STEPS OF WORKSTEPS OF WORK SAMPLINGSAMPLING 3.3. Determine length of sampling periodDetermine length of sampling period 4.4. Conduct work sampling study,Conduct work sampling study, record observationsrecord observations 5.5. Periodically re-compute number ofPeriodically re-compute number of observationsobservations
  • 8. PROCEDUPROCEDU RERE • Preparing for work samplingPreparing for work sampling • Performing work samplingPerforming work sampling • Evaluating & presenting results ofEvaluating & presenting results of work samplingwork sampling
  • 9. WORK SAMPLING STUDYWORK SAMPLING STUDY PLANSPLANS • Determining the observations needed.Determining the observations needed. • Determining observation frequency.Determining observation frequency. • Design the work sampling form.Design the work sampling form. • Observations and data recording.Observations and data recording. • Using control charts to ensure that theUsing control charts to ensure that the observed p values are in-control.observed p values are in-control. • Perform estimation for p value andPerform estimation for p value and continuous improvement.continuous improvement.
  • 10. DETERMINATION OFDETERMINATION OF SAMPLE SIZESAMPLE SIZE          −= = += +≤≤− − = n pq pLCL pCenterline n pq pUCL n qp zpp n qp zp E ppz n 3 3 ˆˆ ˆ ˆˆ ˆ 2 )ˆ1(ˆ2 22 αα
  • 12. ERRORS INERRORS IN WORKWORK SAMPLINGSAMPLING • Observational ErrorsObservational Errors • Experimental ErrorsExperimental Errors
  • 13. CONDUCTING THE WORK SAMPLINGCONDUCTING THE WORK SAMPLING STUDYSTUDY Observ ation Machine idle Machine working Waiting for repairs Waiting for supplies Personal needs Of workers Cutting Boring Filling Idle
  • 14. MAKING THE OBSERVATIONSMAKING THE OBSERVATIONS • Selecting a job to be studied & maintainingSelecting a job to be studied & maintaining the scope of the studythe scope of the study • Making preliminary observations toMaking preliminary observations to determine the approximate value of p fordetermine the approximate value of p for the activitythe activity • In terms of chosen confidence level,In terms of chosen confidence level, determine the number of observationsdetermine the number of observations needed, ‘n’needed, ‘n’ • Designing record sheet to meet theDesigning record sheet to meet the objectives of the studyobjectives of the study
  • 15. USES OF WORK SAMPLINGUSES OF WORK SAMPLING • To aid in determination of time standards &To aid in determination of time standards & delay allowances.delay allowances. • To aid in the measurement of overallTo aid in the measurement of overall performances.performances. • To determine the nature & extent of cycles &To determine the nature & extent of cycles & “Peak Load” Variations in observable activity.“Peak Load” Variations in observable activity. • To study the utilization by supervisors &To study the utilization by supervisors & establishing goals for supervisionestablishing goals for supervision
  • 16. • To aid in job evaluationTo aid in job evaluation • To assist in engineering economyTo assist in engineering economy studiesstudies • To aid in manpower planningTo aid in manpower planning • For appraisal of safetyFor appraisal of safety performance.performance. • For appraisal of organizationalFor appraisal of organizational efficiency.efficiency.