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SCHEDULE LOGIC AND NEGATIVE LAGS (LEADS)

Plenty of differing opinions exist both in favor and against the use of Negative Lags, or Leads, are they also called. The most commonly cited one, not in favor of, is the DCMA 14 point check. Some in the middle eastern region also bank upon Aramco standards, QP standard practices, etc.

Not that these referred standards lack in any respect but critical appraisals of these practices also exist.

What any professional planner should do before leaning either way is to realize that these so-called standards are not universally applicable, accepted, or applied. In most cases they are the standards developed by a particular organization to be applied on its own projects. E.g. DCMA came up with those checks because it had a large number of projects being performed by many different contractors, each with their own way of working. So, they had to ‘standardize’ everything, to be able to reconcile all the information in one collective, homogeneous, meaningful whole. Stretching the point further, different contracting companies have their own productivity lists even if they are working in the same region. Does that make one organization’s standard correct and everyone else’s incorrect? Obviously not. They are all correct where they stand. One is free to evaluate logic and decide whether it also works for them or not.

Have we ever wondered what would our stance have been if some of these organizations had found that negative lags were acceptable? Then there would have been critical appraisals of that acceptance. In short, a coin will always have two sides.

Because of this lack of uniformly or universally accepted principles as noted above, I have taken below some references from a most widely known source (repeat – most widely ‘known’, not universally applicable) – PMI: Practice Standard of Scheduling.

I have found PMI’s approach to be very neutral towards both, i.e. neither favoring not discrediting either, while emphasizing logical approach.

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3.4.9: Leads and lags can introduce schedule risk … It is important to have a clear understanding of consequences that leads and lags can have on a schedule model. … judgement is needed to use the correct method best representing the nature of the activity and the lead or lag.
(refer image)

Miscellaneous notes:

The Not Scored components can be present in a schedule model but are not counted in the conformance index.

The Practice Standard for Scheduling offers a broader scope, increased clarity, and an even higher level of ‘consensus’. (Note: consensus is agreement in general, but not necessarily totality).

Good practice does not mean that the knowledge described should always be applied uniformly on all projects.

As is obvious, the PMI is taking a logical approach to the model. In other words, if logic dictates and justifies the use of Lead or Lag, the same can be used, provided the accompanying implications are well understood. Similarly, constraints are not usually advocated but there may be times when their use becomes absolutely justifiable.

The underlying principle in every case should be logic. Because without logic even a simple FS relationship with zero lag may be incorrect.

As engineering professionals, we must always leave the door open for reason and be amenable to understand the other side’s point of view.
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WHAT IS DATA DATE?

Data Date is the date on which the schedule status is being determined.

For initial schedules it is the project commencement date;

For updates it is the reporting period cut-off date.

e.g. Project-x : start 01-Jan and finish 31-Dec with updates every two weeks.

Baseline (initial schedule), data date = 01-Jan

First Update including progress status for the first two weeks, data date = 15-Jan

Second Update (made on the schedule from First Update) including progress for the next two weeks, data date = 31-Jan
.. and so on.

With every subsequent update the data date (shown as a vertical line on the time scale, usually in blue color) shifts to a later point in time and shows actual accomplishments on its left and remaining work on the right. (refer sample image).

Schedule Levels:

Project participants frequently misunderstand the definition of schedule levels, which limits the quality and value of the information provided to the stakeholders and project participants.

Project participants and stakeholders require different types of data and levels of detail relative to their schedule usage.
The project owner or client is most likely to be interested in milestones and facility/feature start and completion dates at a higher or summary level.

Contractors would monitor and control their subcontractors at an intermediate level and control their direct hire project efforts at a much greater level of detail.

Subcontractors and vendors would typically monitor and control their own work at a task list level, even though they will be required to interface with other subcontractors or vendors and report to the construction manager or prime contractor at a higher level.

Ultimately, the project contract documents, terms and conditions will determine the format and content of the project or program schedule levels.

Traditionally the schedule levels have been identified by a numeric designation.

Level 0: This is the total project and could be a single bar spanning from start to finish or a list of major project milestones.

Level 1: Represents the schedule's major components in relation with the milestones.

Level 2: Each major component is subdivided into broad sub-components.

Level 3: The above mentioned sub-components are further divided into smaller components. This is the first level where a meaningful critical path is displayed.

Levels 4 and higher: When operating at higher, more detailed levels, Planners usually work with segments of the total schedule. A segment or portion of particular interest is taken and broken down into great detail (as much as desired) - micro planning. Such exercises are usually done separately (in spreadsheets or as small but highly detailed schedules for the portion under study).