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Final pres. work sampling (3)


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Final pres. work sampling (3)

  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 12. ERRORS INERRORS IN WORKWORK SAMPLINGSAMPLING • Observational ErrorsObservational Errors • Experimental ErrorsExperimental Errors
  13. 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. 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. 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. 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.