WORK WORK SAMPLINGSAMPLING

BY:BY:

SAURABH SAURABH ARORA,400807034ARORA,400807034

SAMPREET SAMPREET SINGH,400807025SINGH,400807025

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

BASIC CONCEPTS BASIC CONCEPTS & DEFINATION& DEFINATION

Work sampling is a methodology for Work sampling is a methodology for finding the percentage occurrence of finding the percentage occurrence of a certain activity by statistical a certain activity by statistical sampling & random observations.sampling & random observations.

PROBABLITY DISTRIBUTIONPROBABLITY DISTRIBUTION

• Probability based on the binomial Probability based on the binomial distribution distribution (p + q)(p + q)nn = 1 = 1

• Mean = Mean = npnp, Variance = , Variance = npqnpq• As n becomes large, the binomial As n becomes large, the binomial

distribution approaches the normal distribution approaches the normal distributiondistribution

• This proportion has distribution of This proportion has distribution of Mean = Mean = pp, Variance = , Variance = pq/npq/n

STEPS OF WORK STEPS OF WORK SAMPLINGSAMPLING1.1. Define job activitiesDefine job activities

2.2. Determine number of observations Determine number of observations in work samplein work sample

n n = = pp(1 - (1 - pp) ) zzee

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wherewhere

nn = = sample size (number of sample observations) sample size (number of sample observations)zz = = number of standard deviations from mean for number of standard deviations from mean for desired level of confidencedesired level of confidenceee = = degree of allowable error in sample estimate degree of allowable error in sample estimatepp = = proportion of time spent on a work activity proportion of time spent on a work activity estimated prior to calculating work sampleestimated prior to calculating work sample

Example of Sample Size Example of Sample Size CalculationCalculation

• Formula for calculation purposes Formula for calculation purposes simplifies to: n = Zsimplifies to: 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)2n = 225,76 observations

STEPS OF WORK STEPS OF WORK SAMPLINGSAMPLING

3.3. Determine length of sampling Determine length of sampling periodperiod

4.4. Conduct work sampling study, Conduct work sampling study, record observationsrecord observations

5.5. Periodically re-compute number Periodically re-compute number of observationsof observations

PROCEDURPROCEDUREE

•Preparing for work samplingPreparing for work sampling

•Performing work samplingPerforming work sampling

•Evaluating & presenting results Evaluating & presenting results of work samplingof work sampling

WORK SAMPLING STUDY WORK 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 the Using control charts to ensure that the

observed p values are in-control.observed p values are in-control.• Perform estimation for p value and Perform estimation for p value and

continuous improvement.continuous improvement.

DETERMINATION OFDETERMINATION OFSAMPLE SIZESAMPLE SIZE

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PROCEDURE FOR PROCEDURE FOR SELECTING SELECTING RANDOM RANDOM OBSERVATIONSOBSERVATIONS

ERRORS IN ERRORS IN WORK WORK SAMPLINGSAMPLING

•Observational ErrorsObservational Errors

•Experimental ErrorsExperimental Errors

CONDUCTING THE WORK SAMPLING CONDUCTING THE WORK SAMPLING STUDYSTUDY

Observation

Machineidle

Machineworking

Waiting for repairs

Waiting forsupplies

Personal needs

Ofworkers

Cutting Boring Filling Idle

MAKING THE MAKING THE OBSERVATIONSOBSERVATIONS• Selecting a job to be studied & maintaining the Selecting a job to be studied & maintaining the

scope of the studyscope of the study

• Making preliminary observations to determine Making preliminary observations to determine the approximate value of p for the activitythe approximate value of p for the activity

• In terms of chosen confidence level, determine In terms of chosen confidence level, determine the number of observations needed, ‘n’the number of observations needed, ‘n’

• Designing record sheet to meet the objectives Designing record sheet to meet the objectives of the studyof the study

USES OF WORK USES OF WORK SAMPLINGSAMPLING

• To aid in determination of time standards To aid in determination of time standards & delay allowances.& delay allowances.

• To aid in the measurement of overall To 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 & “Peak Load” Variations in observable activity.activity.

• To study the utilization by supervisors & To study the utilization by supervisors & establishing goals for supervisionestablishing goals for supervision

•To aid in job evaluationTo aid in job evaluation

•To assist in engineering To assist in engineering economy studieseconomy studies

•To aid in manpower planningTo aid in manpower planning

•For appraisal of safety For appraisal of safety performance.performance.

•For appraisal of organizational For appraisal of organizational efficiency.efficiency.