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182 USING AND MANAGING CONTINGENCY

defined to the system. If our model has not recognized several activities that
might pop up later (a normal situation), doesn’t the project completion date
have even less than a 50 percent chance? How much time contingency should
we allow for unidentified work?

The point is that we must allow a time cushion. How much of a cushion will
depend on:

• The degree of acceptable risk or penalty for delays.
• How complete the definition of the workscope is.
• How well the work will be managed (if pressure is not kept on the schedule,

slips of up to 50% can be expected).
• How active Murphy is on your job.

The easiest and safest way to build in a time contingency is to extend the proj-
ect end date to a point where there is a comfortable amount of positive float. But
this may not be practical for several reasons. It may not be cost effective. It may
not be acceptable to your client. It may not fit with other programs associated
with your project. However, it is not prudent to proceed with a zero float plan if
meeting the end date is important. Therefore, if the end date can’t be moved,
then the work must be replanned to create a schedule with reasonable positive
float (time contingency). Replanning, to gain schedule float, can involve one or
more of the following:

• Selective overlapping of tasks.
• Increased resources or use of overtime.
• Reducing scope.
• Outsourcing.
• Alternative strategies.

As the available time cushion is reduced, the alternatives are to take preemp-
tive actions to prevent high-risk incidents from occurring, and to increase efforts
to identify all the work as early as possible.

Tip When the schedule contingency is too small to allow
slippage, more effort must be spent on managing task
interfaces. My experience has been that as much time can
be lost between tasks as in the execution of the tasks them-
selves.