Work Sampling
Work sampling is a commonly used industrial engineering technique designed to estimate how resources such as people, machines, facilities, or equipment are being utilized. The objective of work sampling is to assess the workforce utilization of a selected portion of an organization's operations. If an operation is to be audited, work sampling is a low-cost alternative to continuous monitoring, just as sampling in the audit context is a low-cost alternative to 100 percent evaluation of an account. The cost of continuous monitoring of an entire operation is generally prohibitive, and work sampling can yield a reasonably accurate estimate at a fraction of that cost.
Work sampling studies are used by auditors to evaluate a contractor’s labor utilization. When performing a work sampling study, the auditor makes a specified number of observations of contractor personnel involved in the operation being audited. Each observation is classified according to type of activity; the activity types being specified prior to sampling. Using information gathered during the study, the auditor can estimate the percentage of time that the workers actually spend in each activity. With minimal specialized training, an auditor can identify various worker actions and determine whether a contractor’s management practices yield reasonable and acceptable levels of working activity.
Work sampling may disclose underutilized workers, poor work practices, overstaffing, inadequate training, inefficient plant layout, excessive delays (caused by poor planning, material scheduling, or tooling), or other deficiencies.
Definition Working Sampling
- Work sampling is broadly defined as the application of statistical sampling techniques to the study of work activities. In the audit context, work sampling is typically used to estimate the proportion of workers' time that is devoted to different elements of work activity. Work sampling is also known as activity sampling. It can be also used to estimate equipment or vehicle utilization.
- For DCAA applications, the observed activities are grouped into one of two main classifications: working or nonworking.
- The working classification can be subdivided into desirable or undesirable. Hands-on activities like assembling, machining, drawing, designing, etc., are desirable work-related efforts, while waiting for material handlers to move parts, talking to supervisor, activities.
- Nonworking activities include unnecessary delays, needless walking, non-business conversations, personal time, etc. These activities may be broken down further to help identify contributing factors. The degree of detail will depend on the overall objectives of sampling, the type of work environment, and the sampling plan.
Characteristics of work sampling study
The study of work sampling has some general characteristics related to the work condition. One of them is the sufficient time available to perform the study. A work sampling study usually requires a substantial period of time to complete. There must be enough time available (several weeks or more) to conduct the study. Another characteristic is multiple workers. Work sampling is commonly used to study the activities of multiple workers rather than one worker. The third characteristic is long cycle time. The job covered in the study has relatively a long cycle time. The last condition is the non-repetitive work cycles. The work is not highly repetitive. The jobs consist of various tasks rather than a single repetitive task. However, it must be possible to classify the work activities into a distinct number of categories.
Steps in conducting a work sampling study
There are several recommended steps when starting to prepare a work sampling study
- Define the manufacturing tasks for which the standard time is to be determined.
- Define the task elements. These are the defined broken-down steps of the task that will be observed during the study. Since a worker is going to be observed, additional categories will likely be included as well, such as "idle", "waiting for work", and "absent".
- Design the study. This includes designing the forms that will be used to record the observations, determining how many observations will be required, deciding on the number of days or shifts to be included in the study, scheduling the observations, and finally determining the number of observers needed.
- Identify the observers who will do the sampling.
- Star the study. All those who are affected by the study should be informed about it.
- Make random visits to the plant and collect the observations.
- After completing the study, analyze and present the results. This is done by preparing a report that summarizes and analyses all data and making recommendations when required.
Planning the Work Sample
- At the outset, prepare an audit program with audit steps for the preparation of a sampling plan. Be sure to dedicate adequate time and resources to the sampling plan. General steps are as follows:
- Develop audit objective and define the universe.
- Establish familiarity with contractor's operation.
- Choose either the group or individual sampling method.
- Obtain necessary data from contractor (such as organization charts, plant layouts, and shift schedules).
- Determine activity classifications for workers being audited.
- Design observation forms to accumulate and summarize data.
- Conduct a probe to evaluate classifications, estimate nonworking activity, evaluate observation areas, as well as any other required area or activity.
- Establish audit dates and duration.
- Estimate sample size and select audit staff.
- Prepare team folders containing such items as schedules, observation forms, and plant layouts.
- Train audit team observers.
- Estimate the consideration factor.
- The sequence and steps may be altered to fit specific situations as particular audits evolve or may be tailored to suit uniquely different audits.
Defining Audit Objective, Universe, and Work Sampling Method
- The auditor should begin by defining the audit objective. List various reasons for considering work sampling, such as excessive walking, idleness, and poor use of resources. Define the universe (area, population, and work periods) to be studied. These two steps will help clarify and focus the audit. As a part of the audit objective, develop a precise statement of purpose. Data accumulation and savings computations hinge on a precisely defined objective.
- The auditor should become familiar with the target universe. Information sources include facility layouts, organization charts, department charters, product lines, process sheets, and occupation codes. Gather information about support service functions and areas including test labs, CAD/CAM rooms, technical libraries, tool cribs, stock rooms, production/quality control points, and setup and maintenance areas.
- Choose either the individual or group sampling method.
- In individual sampling, for each observation, a worker is randomly selected from the defined population. The activities of the entire defined population are determined based on an analysis of the activities of the randomly selected workers. The advantages of the individual method are as follows:
- Individual sampling allows detailed scrutiny of employee work activities. The observation consists of only one individual worker at a time. Any missing worker in the sample must be accounted for.
- Individual sampling adapts readily to detailed classification of activities. This aids in the analysis of nonworking activities.
- In group sampling, for each observation, the activities of groups of workers from the defined population are recorded. The advantages of the group method are as follows:
- Group sampling requires, at maximum, less than half the time to conduct each observation round. Seeking specific individuals is time consuming.
- Group sampling is less disruptive to the work force because individuals are not singled out for sampling and, unlike individual sampling; no follow-up action to account for missing workers is required. Therefore, discussions with supervisors or co-workers to trace whereabouts of individuals are avoided.
- With group sampling, the potential for worker-induced bias is reduced. Workers are not forewarned, as is likely when specific individuals are sought.
- Select the appropriate sampling plan and selection procedure. The sampling plan can be either simple or stratified, and random sample selection procedure can be either unrestricted or restricted.
- Restricted sample selection generally takes the form of systematic sampling. For a general discussion of random sample selection procedures geared to audit sampling. The concepts are fully applicable to work sampling. Systematic sample selection in work sampling generally is most useful in setting the time when rounds will be made. A fixed time interval between one observation and the next is established. The time interval must be large enough to give the sampler adequate time to make a round at one location and move to the next. The starting time, the time of the first observation, is selected randomly and can be anywhere between a specified minimum and maximum starting time. The difference between the minimum and maximum starting times must equal the fixed time interval the subsequent observations are to be made. Subsequent rounds must be made at fixed intervals from the randomly selected starting time.
- A stratified sampling plan consists of subdividing the universe into strata, which are essentially separate smaller universes. Either simple or systematic selection can be used on the individual strata. There are various reasons for stratification. As discussed in I-400, it enables the sampler to control the number of sample observations that are drawn from specified subsets (strata) of the universe. In group sampling, stratification can yield sample results that are more precise than those of simple random samples of the same sample size. This would be the case when certain areas of activity can be expected to have exceptionally high variation (or wide fluctuation) in non productive activity from one observation to the next. If stratification is done, the strata should be well defined and the conclusions based on the sample from each stratum should be limited to that stratum.
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