Schedule constraints have a significant effect on risk analysis results. They should be used sparingly, and only when the constraint reflects reality. Constraints to be particularly aware of are: • Must start on and Must finish on – preceding delays will not delay the task, and preceding time savings will not bring it earlier • Start on or after (SNET) and Finish on or after (FNET) – preceding time savings will not bring the task earlier Consider removing these constraints and replacing them with logic (e.g. Finish-to-Start links) instead. Other types of constraints are less significant because they do not influence the tasks' dates, only their floats. For example, you can use a Finish on or before constraint to indicate a desired completion date of a task – this will not force the task to finish on that day, but the shortfall will be indicated in the task's float.
Options selected:Predecessors, Successors
For a schedule risk analysis to be meaningful, it is important that tasks' dates are set by logic (e.g. Finish-to-Start links) rather than constraints. This is so that the risk analysis will recognize the knock-on effect of delays. An open-ended task is one that does not have at least one predecessor and one successor – it indicates a possible lack of logic. Consider closing open-ended tasks: • If a task has no predecessor, try to find some other tasks which could potentially delay it. Leave it as open-ended if it is the project start milestone. • If a task has no successors, try to find some other tasks which it could potentially delay. Leave it as open-ended if it is a project finish or reporting milestone.
The logic in a plan can be broken when tasks have started or finished before their predecessors. It is recommended that any broken logic is removed or corrected to ensure the project schedules as expected. For example, if task A has a Finish-to-Start link to task B, but B has been started (by giving it an Actual Start date), this is broken logic. It is not clear whether B's remaining work should wait for task A to finish, or start straight away. Consider fixing the broken logic by either removing the link or removing the actual dates. Also consider using the retained logic / progress override options on the Scheduling tab of the Plan | Options dialog box.
Option selected: Display lags greater then 100 Days
A lag is a gap in the logic between two tasks – a delay between the dates of two tasks that are linked together. Lags cannot have risk or uncertainty. In reality it is likely that the lag represents either work or a delay, whose duration is uncertain. This is particularly significant for long lags. Consider replacing the lag with a task, so that uncertainty and risks can be assessed against it. Use the Convert Lags to Tasks tool when a project contains a large number of long lags.
A negative lag is an overlap in the logic between two tasks – often it is used to represent a task starting earlier, with sufficient time allow some other work to happen. Lags cannot have risk or uncertainty. In reality it is likely that the negative lag represents an necessary overlap, whose duration is uncertain. Consider replacing a negative lag with another kind of link that does not need the lag. For example: • Replace a negative lag on a Finish-to-Start link with a positive lag on a Start-to-Start link. • Split the tasks so that the overlap is explicitly represented by a task.
A lag is a gap in the logic between two tasks – a delay after one task finishes before the next one starts. Lags cannot have risk or uncertainty. In reality it is likely that the lag represents either work or a delay, whose duration is uncertain. Consider replacing the lag with a task, so that uncertainty and risks can be assessed against it. Use the Convert Lags to Tasks tool when a project contains a large number of long lags.
Start-to-Finish links are used deliberately very rarely, because they have the unusual effect that the successor happens before the predecessor. Consider whether this logic might be a mistake, especially if it is between tasks that are not milestones.
A lag is a gap in the logic between two tasks – a delay between the dates of two tasks that are linked together. When the two tasks have different calendars, it is not clear which calendar the task will use – whether it is the preceding task's or the succeeding task's calendar. Consider replacing the lag with a task, so that its calendar can be explicitly defined. Use the Convert Lags to Tasks tool when a project contains a large number of long lags.
Many people prefer not to put predecessors or successors against summary tasks, because other project management tools (such as Primavera P6) do not support them. Consider removing logic on a summary task, by using a milestone to represent the start or finish of all the tasks in the summary heading, and putting the link on the milestone instead of the summary task.
Tasks identified where: Maximum - Most Likely duration divided by the Most Likely - Minimum duration is greater than 2. The validation is only applied to the following distributions:
The check also tells you whether the numbers entered for Min, Most Likely and Max create a valid distribution.
A task's duration can have a "skewed" three-point estimate, which means it is not symmetrical. Usually three-point estimates are skewed on the "pessimistic" side, where the maximum is further away from the most likely than the minimum. The ratio of (Maximum - Most Likely) to (Most Likely - Minimum) is used to measure this skew. When the skew is significant (for example minimum = 1, most likely = 10, maximum = 100), this may be an indication that there are low-probability events that cause this pessimism. Consider using the risk register to represent these risks events, and reduce the amount of skew on the task's uncertainty.