User's Manual

Engineering ACD applications with report data
Issue 5.0 May 2005 109
percent (175 calls per hour yield 10.0 percent, but 160 calls per hour were stated). To get
the delay criterion back to 1.6 percent would require a delay time of about 55 seconds.
Another measure of what is happening with the queue is the average time spent waiting for
service in the queue. With 160 calls per hour, the mean time spent in the queue is 7.53
seconds. With 185 calls per hour, the mean time in the queue is 16.14 seconds. The point
of this example is to emphasize the sensitivity of the time in the queue to the arrival rate. In
other words, increasing the agent efficiency from 67 percent to 77 percent nearly doubles
the various measures of queuing time.
Example 2
Note:
Note: For Examples 2 and 3, the “?s” in the tables represent the unknown values
you are looking for. The italicized numbers in the tables represent numbers
that are not included in the engineering tables.
The reservations department for a hotel chain knows that the average call duration is five
minutes and that most of the potential customers will not wait more than one minute for
their call to be answered. How many agents are required to handle 150 calls per hour?
Under the 60-second column of 300 seconds average service time
on page 131, you will
find the following information:
Therefore, 16 agents are needed to support the reservations department.
Agents 60
14 129
? 150
16 151
y
= number o f agents needed
y
= y
0
+ (y
1
− y
0
)
x
1
− x
0
x − x
0
_ _______
y
= 14 + ( 16 − 14 )
151 − 129
150 − 129
_ _________
y
= 14 + ( 2 × .955 )
y
= 15.9