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WFM Glossary

WFM cycleWorkforce Management definitions and formulas

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Automatic Call Distributor, a part of a PABX that can distribute calls that arrive on one or more numbers to extensions which are part of one or more groups that are assigned to that number.


Average Excess, alternative service level definition, defined as the average time calls wait beyond the AWT.


A step-by-step method to solve a certain, often computational, problem.


Also known as business analytics, a fact-based approach to business process and product improvement using advanced mathematics and ICT.


Average Speed of Answer, the average time a call waits before speaking to an agent.


Acceptable Waiting Time, the target upper bound to the waiting time, very often equal to 20 seconds. Also called Time to Answer (TTA) and Service Time (ST).

Call Center

A collection of resources (typically agents and ICT equipment) capable of delivering services by telephone.


In the context of contact centers a means to have contact with customers. Examples are telephone, fax, and internet.

Contact Center

A collection of resources (typically agents and ICT equipment) capable of delivering services through multiple communication channels.


Customer Relationship Management, mainly used to denote computer systems that allow to record and retrieve interactions with the customer. CRM systems made the advent of call centers possible.

Data Mining

A field of science aimed at discovering relations in data. It has a big overlap with statistics, but it is less mathematical, having its origins in computer science.


First Call Resolution applies when a call is handled right the first time, not necessitating a second call. The FCR rate is the fraction of first calls for which this is the case. See also reconnect.


Information and Communication Technology, technology relative to computers and technology-assisted communication.


Longest idle agent, an agent selection rule used in an ACD mechanism. The agent with the longest idle time since his/her last phone activity (after call work), will be offered the next call.


Longest waiting call, a call selection rule used in multi-skill call centers.


Used throughout the fellowship course as mathematical model, a description in mathematics terms of part of a system, that allows an analysis of certain aspects of that system. For example, a simulation model.


Informal statistical term meaning unexplained variability (as in Poisson noise).


Operations Research, the science that uses mathematical models to improve business operations. Also known as Management Science, therefore sometimes called OR/MS. See also

Predictive Dialer

Functionality of an ACD that allows outbound calls to be automatically initiated, anticipating future availability of agents.


The fact that a caller, after having been served, calls back after some time for the same service. See also FCR.


The fact that a caller, after having been served or not, calls back for the same service. Comprises of redials and reconnects.


Skill(s)-based routing, the fact that different types of calls are routed to different agent groups based on the type of the call and the skills of the agents.

Skill Group

A group of agents all having the same skill set.

Skill Set

The set of skills that an agent or group of agents have.


Service Level, an somewhat ambiguous term that can relate to all aspects of service (waiting time, abandonments, and so forth). In call centers usually defined as the percentage of calls answered within the AWT. Quality of Service is a synonym of the former meaning.


An agent who can only handle one type of call. It can also mean an agent who can do even the most difficult calls, in contrast with a generalist. To avoid ambiguity it is better to use the term single-skilled agent.


Single skill first, an agent selection rule used in multi-skill call centers, that assigns calls to agents with the least number of skills.


Service Time, see AWT.


Time To Answer, see AWT.


Voice Response Unit, synonym to IVR.

Waiting Time

The time a call spends between entering the queue (often after a recorded message, or after having made a choice in a VRU) and an agent being connected to the call.

WFM Tool

A computer tool that assists planners with their WFM tasks. It minimally consists of forecasting, Erlang C, and agent scheduling modules.


Workforce Optimization includes WFM, call monitoring and agent performance management.

Wrap-up Time

Time after the end of a call that the agent spends on the call. Consist usually of entering call-related data in a computer system.


Synonym to cross-trained.


Computer-Telephony Integration, the process that enables communication between and integration of telephone equipment and computer systems.


The prediction of (exogenous) variables such as call volume and AHT

Call Blending

A way of handling different call queues, for example inbound and outbound calls, at the same time by assigning them in a dynamic way to one or multiple agent groups. Call blending is often implemented as a way of maximizing occupancy.

Traffic Management


Private Automatic Branch eXchange, the telephone switch local to the company.


Business-to-business: a commercial transaction between one business and another.


Automatic Number Identification, a technique used to identify customers by their telephone number. Used in combination with CTI to show right away customer information on the agent's computer screen.

Cost Center

In business, a cost center is a division that adds to the cost of an organization, but only indirectly add to its profit. Typical examples include Research and Development, Customer Service and Marketing


Dialed Number Identification Service, a part of the ACD that recognizes the calling number.


First Come First Served, refers to the orders in which queued calls are served: in the order of arrival. Some contact centers practice LIFO -or- Last In First Out principles when handling workload in a busy period


An agent who has all skills and/or can handle all types of calls.


Interactive Voice Response, part of an ACD that allows a customer to enter information by responding to instructions through the keypad of the telephone or the VRU.


  1. In any contact center there is an abundance of metrics. The challenge is to find and use the metrics that matter for your organization.
  2. Examples: Handling time, Occupancy, Shrinkage, Longest Idle Agent, .....
  3. When defining metrics, it all begins with simplicity. If we were to look at our reports and processes, the ways in which we communicate information, and the goals that we target, can we identify the waste? Can we review information we've captured and determine which metrics we've used in meaningful ways versus data we've done nothing with? A great starting point is to sort out which metrics are the "must measures" for contact centers. These include first-contact resolution, service-level and response time, adherence to schedule, forecasting accuracy, self-service accessibility, contact quality, and customer satisfaction. While we should measure additional factors, these metrics are absolute essentials.

Order of Operations

When we speak about operations mathematically, it means things like add, subtract, multiply, divide, squaring, etc. Remember: If it isn't a number it is probably an operation.

When you see something like ...

7 + (6 × 52 + 3)

... what part should you calculate first? 

Start at the left and go to the right? 

Or go from right to left?

Warning: Calculate them in the wrong order, and you will get a wrong answer !

So, long ago people agreed to follow rules when doing calculations, and they are:
Do things in Parentheses First. Example:
yes 6 × (5 + 3)=6 × 8=
no 6 × (5 + 3)=30 + 3=
Exponents (Powers, Roots) before Multiply, Divide, Add or Subtract. Example:
yes 5 × 22=5 × 4=
no 5 × 22=102=
Multiply or Divide before you Add or Subtract. Example:
yes 2 + 5 × 3=2 + 15=
no 2 + 5 × 3=7 × 3=
Otherwise just go left to right. Example:
yes 30 ÷ 5 × 3=6 × 3=
no 30 ÷ 5 × 3=30 ÷ 15=
How Do I Remember It All ... ? PEMDAS !
Parentheses first
Exponents (ie Powers and Square Roots, etc.)
Multiplication and Division (left-to-right)
Addition and Subtraction (left-to-right)



The organizational process of creating and maintaining a plan.

Real-Time Performance Management



Real-Time Performance Management, the activity having as goal on the day of execution to take actions as to obtain the required SL as good as possible.


The process of deciding how to commit resources between a variety of possible tasks.

Short Abandon

A call that is abandoned by the calling party before a connection with an agent is made with 2 conditions:

1. The call is queued 

2. The call is abandoned within a predetermined short abandonment threshold

The reason that short abandons are mentioned separately from regular abandoned calls is short abandons should not be included in service level calculations. The reason behind this line of thinking is that a customer that hangs up within the the short abandonment threshold does not give the contact center agent enough time to pick up the phone. 


Service Level Agreement, the contract between a business unit and higher management or an outsourcer with its client company concerning the required service levels.


The time that an agent is handling calls (talktime plus wrap-up), divided by the total time that the agent is available for handling calls. Utilization and productivity are nowadays often used as synonyms.


The average amount of time customers are willing to wait before abandoning the queue.


Telephone Service Factor, see SL.


The activity of mimicking a real-world system over time, usually performed with a computer. The goal of simulation is to quickly evaluate the performance of such a system, and see how the system behaves by changing some variables. Simulation is also often used to approximate solutions to problems when there is no numerical solution

Net Workload

The number of agent hours needed to handle all incoming calls.

\( Contact Volume \times AHT \)

Remember: When we talk about workload, we mean the actual work that is offered. When we talk about workforce, we mean the capacity to handle the workload that has been offered.

Gross Workforce

Measure of the workforce, which is equal to:

\( Net Workforce + Shrinkage \)

Remember: When we talk about workload, we mean the actual work that is offered. When we talk about workforce, we mean the capacity to handle the workload that has been offered.

Net Workforce

Equal to the Gross Workload

Remember: When we talk about workload, we mean the actual work that is offered. When we talk about workforce, we mean the capacity to handle the workload that has been offered.


The mean (or average) of a series of numbers of length n is defined as the sum of the numbers in the series divided by n. In formula form this is shown as follows:

\( AV = \frac{1}{n} \sum_{i=1}^{n} a_i = \frac{1}{n}(a_1+a_2+a_3+\cdots+a_n) \)

For example: if our series of numbers is 1 2 3 4 5, then the mean is equal to \( \frac{1}{5} \times (1+2+3+4+5) = \frac{1}{5} \times 15 = 3 \).

The excel function for the mean is AVERAGE()

Weighted Mean

The weighted mean is similar to the general mean, except that some points contribute more to the mean than some others. Mathematically if we have a set of points \(a_n\) and a set of weights \(w_n\) that belong to the points, then the weighted average is equal to

\( WAV=\sum_{i=1}^{n}\frac{a_iw_i}{w_i} = \frac{a_1w_1 + a_2w_2 + \cdots + a_nw_n}{w_1+w_2+\cdots+w_n} \)

for example, if we have two sets of points, 1 2 with weight 1 and 3 4 5 with weight 2, then the weighted average of all points is equal to

\( \frac{1 \times 1+2 \times1+3 \times2+ 4 \times2+5 \times2}{1+1+2+2+2}=\frac{1+2+6+8+10}{1+1+2+2+2}=\frac{27}{8}=3.375 \)

In excel there are two ways to calculate the weighted average. say we have the values in column A and the weights in column B.

In the first method we set the product of A and B in column C. Then, the weighted average is given by WAV = SUM(C:C)/SUM(B:B)

The second method uses the sumproduct function. This method doesn't require an additional column to be used. WAV = SUMPRODUCT(A:A,B:B)/SUM(B:B)

Decimal Separator

The Decimal Separator is the charactar used to indicate where the fractional part of a number begins and where the integer part ends.

The symbol used for the ecimal separator differs per country and is either a dot '.' or a comma ','. Because of this, the decimal separator also differs between versions of excel.

On this website we use the English version of excel, therefore we use the dot as the decimal separator.


Amount of work offered to the system, defined by the product of the forecast and the AHT, measured in Erlang.

For example: If the forecast is 4/min and the AHT is 3 minutes, then the load is 4 x 3 = 12 Erlang.


A safety staffing model that, in addition to the Erlang C model, takes abandonments and retrials into account.


The fraction of paid time that an agent is not available for taking calls because of holidays, training, paid breaks, etc.

Below you can see an example of a shrinkage table. It is important to note that this is merely an example to illustrate how shrinkage is calculated. There can be many more activities that can be added and not all activities are relevant for all companies.


A dimensionless unit of load.

For example, if we have a forecasted rate of 4/min and an AHT of 3 minutes, then the load is 4 x 3 = 12 Erlang.

Safety Staffing

The additional number of agents needed to reach a certain service level. The safety staffing level is often calculated by means of the Erlang-C or Erlang-X formulas.


A safety staffing model that takes fluctuations in the number of arrivals and handling times into account.


Workforce Management consists of all activities from forecasting and planning to online control that have to do with the employment of agents in call center.


  1. The amount of hours that is required to handle offered or predicted workload. Because of the need for a safety margin, dictated by theory of variability, more workforce hours are needed than the amount of workload hours.
  2. Net Workforce: the amount of hours required to handle the amount of workload given a certain safety margin
  3. Gross Workforce: the total amount of hours that needs to be paid for.


Business-to-Consumer. A commercial transaction between a business and a consumer.


Denotes an agent who has more than one skill, who can therefore handle more than one type of call. A generalist is fully cross- trained. Also denoted as X-trained.

Gross Workload

The net workload plus a safety:

\(Contact Volume \times AHT + Safety Staff\)

Remember: When we talk about workload, we mean the actual work that is offered. When we talk about workforce, we mean the capacity to handle the workload that has been offered.


Average Handling Time:
  1. The average handle time that is needed to handle 1 quantity of work, usually a call, an email or a chat.
  2. Handling Time and Average Handling Time are two different concepts
  3. The AHT for calls is often calculated over the following PABX metrics

\(AHT= Ringtime + Talktime + Holdtime + Transfertime + Wrapuptime\)


Workload is defined as the amount of work in hours. Workload is usually calculated by the following formula:

\( Workload = Contact Volume \times Average Handling Time \)

Obviously the amount of offered and handled workload can differ over the same interval.


The fact that a caller, after having abandoned or being blocked, calls back after some time for the same service. See also abandonment.

Abandoned Call

A call that is interrupted by the customer that initiated the call before contact with an agent was made. See also redial.


An employee who works in a Call Center, also called (Call Center) representative ('rep'), or CSR (customers sales representative).