JOB DESIGN Work Measurement

Definitions Work measurement - A process of determining the time that a qualified worker should take to complete a job under normal working condition. Qualified worker – A person who has the necessary physical and mental attributes and at the same time has the appropriate skills and tools to perform the job. Time – the length of time taken to complete the job; usually expressed as labor standard or standard time. Normal working condition – the acceptable working environment in term of temperature, humidity, lighting, noise, etc needed to perform the job.

Objectives of work measurement To establish a labor standard that is the time taken by a qualified worker to perform a job. To produce one unit of output by taking into consideration allowances, e.g. time to relax and overcome fatigue, time to setup and warm up machine, etc.

Uses of labor standard Labor standard is useful in determining the following: Expected production Staffing needs Labor costs Cost and time estimates prior to production Job scheduling Basis of wage incentive plan Efficiency of employees and supervision

Work measurement methods Historical experience Time study Predetermined time standard Work sampling

Historical experience Data used to establish standard time is taken from past experience or data; ie. the time required to do a task the last time it was performed. Data is usually available from employee time card or production records Advantage: Relatively easy and inexpensive to obtain Disadvantage: Established time may not be accurate (working pace, unusual occurrence)

Time study A classical stopwatch study proposed by Frederick W. Taylor The most widely used time study method today Especially appropriate for short, highly detailed and repetitive tasks Involves timing a sample of a worker’s performance and using it to set a standard. A trained and experienced person can establish a standard by following the eight steps: Define the tasks to be studied Divide the task into precise elements Decide how many times to measure the task (the number of job cycles or samples needed) Time and record the elemental times and ratings of performance.

Time study – cont. Compute the average observed time (the average time taken to complete each job element after it has been adjusted for any unusual influence) (Sum of the times recorded Average observed time = to perform each element) Number of each observations Determine performance rating (work pace) and compute the normal time/basic time (the mean observed time taken to perform each job element by taking into consideration normal working pace) Normal time = (AOT)(PRF)(F) The PRF adjusts the observed time to what a normal worker could expect to achieve.

Time study – cont. PR of 100% - normal work pace PR > 100% - means the observed worker performs the task faster than average Add the normal time for each element to develop a total normal time for the task.

Time study – cont. 1 – allowance factor vii. Compute the standard time (The adjusted normal time that is the time taken by a qualified worker to complete a job by considering allowances; e.g. personal needs, unavoidable work delays, and worker fatigue. (Eq.1) Standard time = Normal time (1 + Allowance) or (Eq. 2)Standard time = Total normal time 1 – allowance factor Eq. 1 is most often used in practice. (Allowances are based on the job time, used when diff. jobs have diff. allowances) If allowances are based on a percentage of time worked (the workday), and jobs are similar and have the same allowance factors. eq. 2 is the correct one. (9 min. diff.)

Time study – cont. Common type of allowances Personal needs – washroom and coffee breaks, usually established in the range of 4% to 7% of total time, depending on nearness to rest rooms, water fountains, and other facilities Fatigue – physical or mental Unavoidable work delays – machine warm-up, adjustments and repairs, talking to a supervisor or waiting for materials Relaxation allowance – personal needs & fatigue Contingency allowance – unavoidable work delays Process allowance Policy allowance

Time study – cont. The sample size (the number of cycles that must be timed depends on: The variation that exists within the job elements (e.g. if the variation is large, a larger sample will be required) The desired accuracy level The desired level of confidence n = z.s 2 or n = Z.s 2 a. x e where z = number of standard deviations required for desired level of confidence s = standard deviation of the initial sample h or a = desired accuracy level x = mean of the initial sample e = the absolute amount of acceptable error Managerial decision

appropriate sample size if the standard time for Time study – cont. The following data are the standard deviation and the mean observed time derived based on 10 initial observations done on 7 work elements. Determine the appropriate sample size if the standard time for any work element is to be within 5% of the true mean 95% of the time. Element s (min) MOT (min) 1 0.010 0.12 2 0.030 0.25 3 0.040 0.50 4 0.005 5 0.035 0.30 6 0.025 7 0.24

Time study – cont. Element Observation 1 11 2 23 3 10 4 5 21 6 16 7 25 The appropriate number of observations will be 25, meaning that 15 additional observations need to be carried out in order to develop the time standard. After the additional observations are done, new mean observed times need to be calculated for each work element.

Time study – cont. Desired confidence (%) z-value 90.0 1.65 95.0 1.96 90.0 1.65 95.0 1.96 95.45 2.00 99.0 2.58 99.73 3.00 s = Σ (xi – x)2 = Σ (each sample observation – x)2 n-1 n-1 xi = value of each observation x = mean of the observations n = number of observations in the sample

Time study – cont. Observation Time 1 1.7 2 1.6 3 1.5 Observation xi x 0.1 0.01 2 3 1.5 -0.1 Σ 4.8 0.02 s = Σ (xi – x)2 = .02 = 0.1 n-1 2 Assume: 99% confidence level, z = 2.58 h = 3% n = z.s 2 a. x

Time study – cont. Advantages Disadvantages Provide accuracy in setting labor standards Disadvantages Requires a trained staff of analysts (the analysts should be thoroughly familiar with the job and need to check that the job is being performed efficiently before setting the time standard) Labor standards cannot be set before tasks are actually performed thus may interrupt worker at work It is not appropriate for most managerial and creative jobs Not cost effective for irregular operations / non-repetitive jobs

Elemental time data Establishes standards based on previously completed time studies, stored in an organizations’ database Procedures: Identify the standard elements of the job. Check the database for time studies done on these elements. If no valid studies exist for this or a similar work element, do a time study for the new work element. Adjust the database times if needed. E.g. develop an element time by interpolating between two values. Add the element times to determine the normal time, then multiply by the allowance factor to determine the standard time

Elemental time data Advantages Disadvantages Minimize the number of time studies conducted Eliminate the workplace disruption caused by making time studies Disadvantages May discourage new process development and improvements

Predetermined time study Involved dividing manual work into small basic elements that already have established times. The most common PTS is methods time measurement (MTM) PTS are an outgrowth of basic motion called “therbligs” developed by Frank Gilbreth Steps to establish standard time Divide a job into its basic elements (e.g. search, grasp, hold) Measure the distances involved (if applicable) Rate the difficulty of the element Add the time factors for each basic element of that task (The basic elements are measured in TMUs - one TMU equals to 0.0006 minutes or 0.00001 hour)

Predetermined time study – cont. Advantages Data are based on large number of workers under controlled conditions Performance rating is not required No disruption of operation (as it can be established in lab environment) Standards can be established even before the job is done (useful for planning) Unions tend to accept this method as a fair means of setting standards Especially effective in firms that do substantial numbers of studies of similar tasks

Predetermined time study – cont. Disadvantages Work must be broken into its basic elements – a typical job may involve several hundred or more basic elements Considerable skills are needed to adequately describe the operation Data cannot be generalized to activities in all plants as what is a norm in one plant may not be a norm in another plant. Subjectivity in rating the degree of job element difficulty, etc.

Work sampling Developed in England by L.Tippet in the 1930s Estimates the percent of the time that a worker spends on various tasks Requires random observations to record the activity that a worker is performing Refer “chase”

Work sampling – cont. Applications of work measurement * Ratio delay to determine the activity time percentage for personnel or equipment. E.g. Amount of time a machine is running or idle Performance measurement to develop a performance index for workers. When the amount of work time is related to the quantity of output, a measure of performance is developed. This is useful for periodic performance evaluation. Time standards to obtain the standard time for a task. * Knowledge of this allocation of time may lead to staffing changes, reassignment of duties, estimate of activity costs, and the setting of delay allowance for labor standard

Work sampling – cont. Work sampling procedures: Take a preliminary sample to obtain an estimate of the parameter value (e.g. percent of time a worker is busy) Compute the sample size required Prepare a schedule for observing the worker at appropriate times. (uses random observation) Observe and record worker activities Determine how workers spend their time (usually as a percent)

Work sampling – cont. n = z2 p(1-p) h2 where z = number of standard normal deviations for the desired confidence level p = estimated value of sample proportion (of time worker is observed busy or idle h = acceptable error level, in percent

Work sampling – cont. Total time 480 min Number of parts produced 420 pieces Working time in percent 85% Idle time in percent 15% Avg. performance index 110% Total allowances Deriving a time standard using work sampling Normal time = (Tot. time in min.) x (working time (%)) x PR Tot. no of pieces produced Standard time = Normal time x 1/(1-A) = 480 x 0.85 x 1.10 x 1 = 1.26 minutes 420 1 - 0.15

Work sampling – cont. Advantages (over time study methods) Less expensive as a single observer can observe several workers simultaneously Observers do not require much training No timing devices are needed Observations are spread over a period of time, making results less susceptible to short term fluctuations Worker has little chance of affecting the study’s outcome as it uses random observations over a long period The procedure is less intrusive and thus less likely to generate objections Studies can be interrupted without affecting the results It is well suited for non repetitive tasks Work of a long cycle time may be studied with fewer observer hours

Work sampling – cont. Disadvantages It does not divide work elements as completely as time studies Observers may fail to adhere to a random schedule of observations resulting in biased or incorrect results Because it is less intrusive, it tends to be less accurate; this is particularly true when job element times are short (Not well suited to short, repetitive tasks)