Which of the following is a basic difference of work sampling compared to a time study?

The fundamental purpose of work measurementJob analysis for the purpose of setting time standards. is to set time standards for a job. Such standards are necessary for four reasons:

1. To schedule work and allocate capacity.   All scheduling approaches require some estimate of how much time it takes to do the work being scheduled.

2. To provide an objective basis for motivating the workforce and measuring workers' performance.   Measured standards are particularly critical where output-based incentive plans are employed.

3. To bid for new contracts and to evaluate performance on existing ones.   Questions such as “Can we do it?” and “How are we doing?” presume the existence of standards.

4. To provide benchmarks for improvement.   In addition to internal evaluation, benchmarking teams regularly compare work standards in their company with those of similar jobs in other organizations.

Work measurement and its resulting work standards have been controversial since Taylor's time. Much of this criticism has come from unions, which argue that management often sets standards that cannot be regularly achieved. (To counter this, in some contracts, the industrial engineer who sets the standard must demonstrate that he or she can do the job over a representative period of time at the rate that was set.) There is also the argument that workers who find a better way of doing the job get penalized by having a revised rate set. (This is commonly called rate cutting.)

With the widespread adoption of W. Edwards Deming's ideas, the subject has received renewed criticism. Deming argued that work standards and quotas inhibit process improvement and tend to focus the worker's efforts on speed rather than quality. Of course, standards and process improvement need not be mutually exclusive, as Toyota and its Kaizen has shown. (See Breakthrough box.)

Despite these criticisms, work measurement and standards have proved effective. Much depends on sociotechnical aspects of the work. Where the job requires work groups to function as teams and create improvements, worker-set standards often make sense. On the other hand, where the job really boils down to doing the work quickly, with little need for creativity (such as delivering packages for UPS), tightly engineered, professionally set standards are appropriate.

WORK MEASUREMENT TECHNIQUES

There are four basic techniques for measuring work and setting standards. These consist of two direct observational methods and two indirect methods: The direct methods are time studySeparation of a job into measurable parts, with each element timed individually. The individual times are then combined, and allowances are added to calculate a standard time., which uses a stopwatch to time the work, and work samplingAnalyzing a work activity by observing an activity at random times. Statements about how time is spent during the activity are made from these observations., which entails recording random observations of a person or teams at work. The two indirect methods are predetermined motion-time data systems (PMTS)Systems for deriving a time for a job by summing data from tables of generic movement times developed in the laboratory., which sum data from tables of generic movement times developed in the laboratory to arrive at a time for the job (the most widely used are proprietary systems—Methods Time Measurement [MTM] and Most Work Measurement System [MOST]), and elemental dataUsed to derive a job time by summing times from a database of similar combinations of movements., which sums times from a database of similar combinations of movements to arrive at job time. The choice of techniques depends on the level of detail desired and the nature of the work itself. Highly detailed, repetitive work usually calls for time study and predetermined motion-time data analysis. When work is done in conjunction with fixed-processing-time equipment, elemental data are often used to reduce the need for direct observation. When work is infrequent or entails a long cycle time, work sampling is the tool of choice. (See box “What the Pros Say…About Work Measurement Applications in Retailing” for an example of how the different techniques are used in a service setting.)

BREAKTHROUGH

HOW TOYOTA USES WORK STANDARDS The Toyota managers who share their insights with us say there are two simple rules that are part of every Toyota employee's job. They are Follow the standard. Find a better way. This is the essence of Kaizen. Kaizen is a Japanese expression for “continuous improvement of processes.” These simple yet profound rules are what drive every employee to maintain safety, quality, low cost, and on-time, and further strive to make it better. (K) At Toyota's North American Production Support Center In Georgetown, KY, Toyota plant managers are trained as part of the company's global initiative to share best practices worldwide. Taiichi Ohno, the godfather of the Toyota Production System, said, “Where there is no standard, there can be no kaizen (improvement).” When the fastest, safest, best quality, repeatable steps have been identified, this is documented as the standard. That is now the record to beat. Kaizen teams find and eliminate unreasonable/unsafe working conditions and eliminate waste and variability. The term “standard” can be misunderstood as something rigid, unchanging, and absolute. If it is misunderstood in this way, it becomes an obstacle to Kaizen. Take the example of a first-tier automotive supplier of rubber products. After redesigning the assembly lines and implementing one-piece flow, it came time to create Standard Work procedures. The production manager who had been actively participating in Kaizen resisted documenting Standard Work. When finally confronted, he explained that he didn't want a published standard time because he wanted to keep challenging guys to beat their times and get higher production in fewer hours. What he was talking about was “the record” you had to beat to have your picture up on the “wall of fame” at the factory. Standard Work is the method used to achieve that record and must be redrawn each time the record is broken. It is how you train to beat the new record. Machine operators in a candy factory had concerns with establishing standards settings on their production lines. Their reasoning had to do with the fact that, in the past, management had wanted the standard followed strictly and not adjusted. This was an attempt to maintain control and keep quality at a certain level. Yet without the “Find a better way” element, it was not Kaizen. Source: Adapted From Jon Miller, “The Toyota Job Description: Follow Standards & Find Better Ways,” Gemba Panta Rei Web log, www.gembapantarei.com.

TIME STUDY

We now turn to a discussion of the technical details of time study. A time study is generally made with a stopwatch, either on the spot or by analyzing a videotape for the job. The job or task to be studied is separated into measurable parts or elements, and each element is timed individually.

Some general rules for breaking down the elements are

1. Define each work element to be short in duration but long enough so that it can be timed with a stopwatch and the time can be written down.

2. If the operator works with equipment that runs separately (meaning the operator performs a task and the equipment runs independently), separate the actions of the operator and of the equipment into different elements.

3. Define any delays by the operator or equipment into separate elements.

After a number of repetitions, the collected times are averaged. (The standard deviation may be computed to give a measure of variance in the performance times.) The averaged times for each element are added, yielding the performance time for the operator. However, to make this operator's time usable for all workers, a measure of speed or performance rating must be included to “normalize” the job. The application of a rating factor gives what is called normal timeThe time that a normal operator would be expected to take to complete a job without the consideration of allowances.. For example, if an operator performs a task in two minutes and the time-study analyst estimates her to be performing about 20 percent faster than normal, the operator's performance rating would be 1.2, or 120 percent of normal. The normal time would be computed as 2 minutes × 1.2, or 2.4 minutes. In equation form,

Normal time = Observed performance time per unit × Performance rating

In this example, denoting normal time by NT,

NT = 2(1.2) = 2.4 minutes

When an operator is observed for a period of time, the number of units produced during this time, along with the performance rating, gives

Standard timeCalculated by taking the normal time and adding allowances for personal needs, unavoidable work delays, and worker fatigue. is derived by adding to normal time allowances for personal needs (such as washroom and coffee breaks), unavoidable work delays (such as equipment breakdown or lack of materials), and worker fatigue (physical or mental). Two such equations are

Standard time = Normal time + (Allowances × Normal time)

or

ST = NT (1 + Allowances)   [6A.1]

and

Equation (6A.1) is most often used in practice. If one presumes that allowances should be applied to the total work period, then equation (6A.2) is the correct one. To illustrate, suppose that the normal time to perform a task is one minute and that allowances for personal needs, delays, and fatigue total 15 percent; then by equation (6A.1)

ST = 1(1 + 0.15) = 1.15 minutes

In an eight-hour day, a worker would produce 8 × 60/1.15, or 417 units. This implies 417 minutes working and 480 − 417 (or 63) minutes for allowances.

With equation (6A.2),

In the same eight-hour day, 8 × 60/1.18 (or 408) units are produced with 408 working minutes and 72 minutes for allowances. Depending on which equation is used, there is a difference of nine minutes in the daily allowance time.

EXAMPLE 6A.1: Time Study for a Four-Element Job

Exhibit 6A.3 shows a time study of 10 cycles of a four-element job. For each element, there is a space for the watch readings that are recorded in 100ths of a minute. Space also is provided for summarizing the data and applying a performance rating.

Exhibit 6A.3	Time-Study Observation Sheet
(K)

SOLUTION

The value of

Exhibit 6A.4	Guide to Number of Cycles to Be Observed in a Time Study
(K) Source: B. W. Niebel, Motion and Time Study, 9th ed. (Burr Ridge, IL: Richard D. Irwin, 1993), p. 390. The McGraw-Hill Companies, Inc. Used with Permission.

WORK SAMPLING

A second common technique for measuring a job is called work sampling. As the name suggests, work sampling involves observing a portion or sample of the work activity. Then, based on the findings in this sample, statements can be made about the activity. For example, if we were to observe a fire department rescue squad at 100 random times during the day and found it was involved in a rescue mission for 30 of the 100 times (en route, on site, or returning from a call), we would estimate that the rescue squad spends 30 percent of its time directly on rescue mission calls. (The time it takes to make an observation depends on what is being observed. Many times, only a glance is needed to determine the activity, and the majority of studies require only several seconds' observation.)

Observing an activity even 100 times may not, however, provide the accuracy desired in the estimate. To refine this estimate, three main issues must be decided. (These points are discussed later in this section, along with an example.)

1. What level of statistical confidence is desired in the results?

2. How many observations are necessary?

3. Precisely when should the observations be made?

The three primary applications for work sampling are

1. Ratio delay to determine the activity-time percentage for personnel or equipment. For example, management may be interested in the amount of time a machine is running or idle.

2. 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.

3. Time standards to obtain the standard time for a task. When work sampling is used for this purpose, however, the observer must be experienced because he or she must attach a performance rating to the observations.

The number of observations required in a work-sampling study can be fairly large, ranging from several hundred to several thousand, depending on the activity and desired degree of accuracy. Although the number can be computed from formulas, the easiest way is to refer to a table such as Exhibit 6A.5, which gives the number of observations needed for a 95 percent confidence level in terms of absolute error. Absolute error is the actual range of the observations. For example, if a clerk is idle 10 percent of the time and the designer of the study is satisfied with a 2.5 percent range (meaning that the true percentage lies between 7.5 and 12.5 percent), the number of observations required for the work sampling is 576. A 2 percent error (or an interval of 8 to 12 percent) would require 900 observations.

Exhibit 6A.5	Number of Observations Required for a Given Absolute Error at Various Values of p, with 95 Percent Confidence Level
(K)

Five steps are involved in making a work-sampling study:

1. Identify the specific activity or activities that are the main purpose for the study. For example, determine the percentage of time that equipment is working, idle, or under repair.

2. Estimate the proportion of time of the activity of interest to the total time (e.g., that the equipment is working 80 percent of the time). These estimates can be made from the analyst's knowledge, past data, reliable guesses from others, or a pilot work-sampling study.

3. State the desired accuracy in the study results.

4. Determine the specific times when each observation is to be made.

5. At two or three intervals during the study period, recompute the required sample size by using the data collected thus far. Adjust the number of observations if appropriate.

The number of observations to be taken in a work-sampling study is usually divided equally over the study period. Thus, if 500 observations are to be made over a 10-day period, observations are usually scheduled at 500/10, or 50 per day. Each day's observations are then assigned a specific time by using a random number table.

EXAMPLE 6A.2: Work Sampling Applied to Nursing

SOLUTION

Assume at the outset that we have made a list of all the activities that are part of nursing and will make our observations in only two categories: nursing and nonnursing activities. Actually, there is much debate on what constitutes nursing activity. For instance, is talking to a patient a nursing duty? (An expanded study could list all nursing activities to determine the portion of time spent in each.) Therefore, when we observe during the study and find the nurse performing one of the duties on the nursing list, we simply place a tally mark in the nursing column. If we observe anything besides nursing activities, we place a tally mark in the nonnursing column.

We can now plan the study. Assume that we (or the nursing supervisor) estimate that nurses spend 60 percent of their time in nursing activities. Assume that we would like to be 95 percent confident that findings of our study are within the absolute error range of ±3 percent; that is, if our study shows nurses spend 60 percent of their time on nursing duties, we want to be 95 percent confident that the true percentage lies between 57 and 63 percent. From Exhibit 6A.5, we find that 1,067 observations are required for 60 percent activity time and ±3 percent error. If our study is to take place over 10 days, we start with 107 observations per day.

To determine when each day's observations are to be made, we assign specific numbers to each minute and use a random number table to set up a schedule. If the study extends over an eight-hour shift, we can assign numbers to correspond to each consecutive minute. For this study, it is likely the night shift would be run separately because nighttime nursing duties are considerably different from daytime duties. Exhibit 6A.6A shows the assignment of numbers to corresponding minutes. For simplicity, because each number corresponds to one minute, a three-number scheme is used, with the second and third numbers corresponding to the minute of the hour. A number of other schemes would also be appropriate. If a number of studies are planned, a computer program may be used to generate a randomized schedule for the observation times.

Exhibit 6A.6	Sampling Plan for Nurses' Activities
Assignment of Numbers to Corresponding Minutes Determination of Observation Times Observation Schedule (K)

If we refer to a random number table and list three-digit numbers, we can assign each number to a time. The random numbers in Exhibit 6A.6B demonstrate the procedure for seven observations.

This procedure is followed to generate 107 observation times, and the times are rearranged chronologically for ease in planning. Rearranging the times determined in Exhibit 6A.6B gives the total observations per day shown in Exhibit 6A.6C (for our sample of seven).

To be perfectly random in this study, we should also “randomize” the nurse we observe each time. (The use of various nurses minimizes the effect of bias.) In the study, our first observation is made at 7:13 a.m. for Nurse X. We walk into the nurse's area and, on seeing the nurse, check either a nursing or a nonnursing activity. Each observation need be only long enough to determine the class of activity—in most cases only a glance is needed. At 8:04 a.m. we observe Nurse Y. We continue in this way to the end of the day and the 107 observations. At the end of the second day (and 214 observations), we decide to check for the adequacy of our sample size.

Let us say we made 150 observations of nurses working and 64 of them not working, which gives 70.1 percent working. From Exhibit 6A.5, this corresponds to 933 observations. Because we have already taken 214 observations, we need take only 719 over the next eight days, or 90 per day.

When the study is half over, another check should be made. For instance, if days 3, 4, and 5 showed 55, 59, and 64 working observations, the cumulative data would give 328 working observations of a total 484, or a 67.8 percent working activity. For a ±3 percent error, Exhibit 6A.5 shows the sample size to be about 967, leaving 483 to be made—at 97 per day—for the following five days. Another computation should be made before the last day to see if another adjustment is required. If after the 10th day several more observations are indicated, these can be made on day 11.

If at the end of the study we find that 66 percent of nurses' time is involved with what has been defined as nursing activity, there should be an analysis to identify the remaining 34 percent. Approximately 12 to 15 percent is justifiable for coffee breaks and personal needs, which leaves 20 to 22 percent of the time that must be justified and compared to what the industry considers ideal levels of nursing activity. To identify the nonnursing activities, a more detailed breakdown could have been originally built into the sampling plan. Otherwise, a follow-up study may be in order.•

As mentioned earlier, work sampling can be used to set time standards. To do this, the analyst must record the subject's performance rate (or index) along with working observations. Exhibit 6A.7 gives a manufacturing example that demonstrates how work sampling can be used for calculating standard time.

Exhibit 6A.7	Deriving a Time Standard Using Work Sampling
(K)

WORK SAMPLING COMPARED TO TIME STUDY

Work sampling offers several advantages:

1. Several work-sampling studies may be conducted simultaneously by one observer.

2. The observer need not be a trained analyst unless the purpose of the study is to determine a time standard.

3. No timing devices are required.

4. Work of a long cycle time may be studied with fewer observer hours.

5. The duration of the study is longer, which minimizes effects of short-period variations.

6. The study may be temporarily delayed at any time with little effect.

7. Because work sampling needs only instantaneous observations (made over a longer period), the operator has less chance to influence the findings by changing his or her work method.

BREAKTHROUGH

LINKING STANDARDS AND INCENTIVES AT THE GAP DISTRIBUTION CENTERS Fashion retailer The Gap, Inc., believes strongly in the value of engineered labor standards, which have been implemented in some Gap distribution centers for more than a decade. The retailer has engineered labor standards in place for receiving, stocking, order filling, and shipping. These standards “are our number one means of communication” with warehouse associates, explains Jay Ninah, senior planning engineer for The Gap. Reports on individual and group performance are posted weekly and associates meet with their supervisors on a monthly basis to discuss their performance. As a result, associates always know what level of performance is expected of them and how their individual performance compares to the standard. (K) Posting individual as well as group performance data keeps with The Gap's open-book policy, Ninah says. “It's not there to intimidate anyone, but to share our findings. It also creates an expectation that the standards are correctly set. If 85 percent to 90 percent are achieving the standard, those not meeting the standard can determine whether they're using a method that's not the best one.” The Gap coaches based on its standards. Ninah states, “As we identify lower-performing individuals, we have a structured coaching process,” whereby supervisors work with associates on the areas they need to improve. Associates have an extra push to improve their work, thanks to an incentive program tied to performance. The program was pioneered last year, Ninah says, and is getting a good response from associates. “Instead of giving an across-the-board increase, we give it based on performance,” he says. GLOBAL STANDARDS, LOCAL APPLICATION The Gap's distribution network is made up of 18 facilities that range from brand-new warehouses with the latest technology to others that are 20 years old. To make sure that the labor standards are appropriate for each facility, The Gap's central engineering group in Erlanger, Kentucky, creates global standards. These are then localized to fit each distribution center by engineers that work in that facility. Most of The Gap's labor standards are derived largely by using predetermined labor standards using the MOST system developed by H. B. Maynard Co., Ninah says. They are then validated with stopwatch studies. A handful of standards not included in the predetermined time measures have to be completely developed by the engineering staff. STANDARDS TO BUILD ON The standards are a key planning and scheduling tool for The Gap and have proven to be very valuable when setting up new distribution centers. “It gives us a good gauge of how many people we need to hire,” Ninah reports. They also use the labor standards to track a new facility's learning curve. “We're able to see how long it takes a new distribution center to get up to speed,” he says, and for associates to learn their jobs. The standards have proven to be a powerful communication tool for new facilities. The engineering staff develops labor standards for a new distribution center before it opens. The measures enable associates to “understand what's expected of them, and where they are with respect to where they should be,” Ninah says. “We used to expect a six- to eight-month learning curve. Now, it's about half that.” Source: Modified from Distribution Center Management 2002, Alexander Communications Group, Inc., www.distributiongroup.com.

When the cycle time is short, time study is more appropriate than work sampling. One drawback of work sampling is that it does not provide as complete a breakdown of elements as time study. Another difficulty with work sampling is that observers, rather than following a random sequence of observations, tend to develop a repetitive route of travel. This may allow the time of the observations to be predictable and thus invalidate the findings. A third factor—a potential drawback—is that the basic assumption in work sampling is that all observations pertain to the same static system. If the system is in the process of change, work sampling may give misleading results.

How does work sampling differ from time study?

Which of the following is one of the advantages of work sampling over time study methods?

What does work measurement determine?

What is a technique for estimating the proportion of time an employee or machine spends on different work activities?