This week I spent a considerable amount of time trawling through various guidelines and standards to prepare some future articles. In passing through a copy of of the 5th version of the Project Management Body of Knowledge (PMBOK), I almost fell off my chair.

Section 6.3.2.3 talks about "Leads and Lags" and to my disgust makes note of Negative Lag. It appears that the PMBOK and it's writers actually condone the use of lazy planning techniques!

"A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity. For example, on a project to construct a new office building, the landscaping could be scheduled to start two weeks prior to the scheduled punch list completion. This would be shown as a finish-to-start with a two-week lead as shown in Figure 6-10. Lead is often represented as a negative value for lag in scheduling software." [PMBOK Guide, 5th Edition]

Ask just about any experienced Project Planner and they will tell you a raft of reasons why you shouldn't use such logic, however to my own knowledge I haven't seen anyone actually give a good reason why. So a while back I compiled a whitepaper that explains why Negative Lag is a poor form of logic and used an example to prove it.

In summary, here are the reasons we shouldn't use this form of logic:

  1. The lag used is negative and contradicts the logic that is intended to be used in the software
  2. The lead time used can (and should) be represented by an activity which is more controllable
  3. Whilst using negative lag in initial programs may be acceptable in some organisations, they quickly provide inaccurate results once logic is applied

Using negative lag puts your schedule at risk of being able to 'model'progress correctly. Don't use it, don't be lazy, plan properly and for heavens sake, would someone update that section of the PMBOK!

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