Analyzing and understanding the distribution of Total Float (TF) values in a CPM network can be a very revealing and useful indicator. In general, CPM networks with a more “Stressed” Distribution tend to be more sensitive to Project delays as compared to networks with a more “Relaxed” Distribution.
Zümmer’s Float Distribution Curve analysis report provides a graphical chart that can help you quickly determine the condition of the CPM Network. The generated graph plots the Total Float Values along the X-Axis, while the Y-Axis plots a Percentile value indicating the percentage of Tasks that have the X-Axis Float Value or less.
In the illustration below, for the “Stressed” Distribution graph, the range of Total Float Values is from 0 to about 1,210 (along the X-Axis) for the 2,243 Tasks distributed. However, at the 50% Percentile point (along the Y-Axis); the Total Float Value is about 50. In other words, about half of all the Tasks (approximately 1,121 Tasks) in this Project have a Total Float Value of 50 or less.
Similarly, in the illustration below, for the “Relaxed” Distribution graph, the range of Total Float Values is from 0 to about 870 (along the X-Axis) for the 2,725 Tasks distributed. However, at the 50% Percentile point (along the Y-Axis); the Total Float Value is about 175. In other words, about half of all the Tasks (approximately 1,362 Tasks) in this Project have a Total Float Value of 175 or less.
In comparison, and all else being equal, Projects with “Stressed” distribution are more likely to experience delays as compared to Projects with “Relaxed” distribution.
Determining a “Rule-of-Thumb” is subject to debate, however, by observation, Float Distribution Curves that are steep on the left side and flat on the right side, generally fall in the “Stressed” category. Whereas, Float Distribution Curves that are smooth from beginning to end generally fall in the “Relaxed” category.
Very Stressed distributions could be a cause for alarm since this may indicate a Project schedule that is “Claims oriented”. In these cases, you may want to consider reviewing the Project’s overall logic schema to determine where relationships can be removed or revised thereby increasing overall Total Float values.
Very Relaxed distributions could also be a cause for alarm since this may indicate a Project schedule that is insufficiently developed. In these cases, you may want to consider reviewing the Project’s overall logic schema to determine where relationships can be added or revised thereby decreasing overall Total Float values.
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