Appendix VI: Standard Quantitative Measurements for Assessing Schedule Health
An assessment of schedule best practices encompasses both qualitative and quantitative information. Qualitative information is provided by program questions such as those detailed in appendix II. These questions are related to the general policies in place and procedures undertaken to create and maintain the schedule. The quantitative assessment involves a detailed analysis of the schedule data to determine the overall health of the network. While the questions addressed by the data analysis are also covered in appendix II, the quantitative assessment often involves filters and detailed data metric definitions. These filters and definitions are in table 11 for each best practice.
No “pass-or-fail” thresholds or tripwires are associated with the measures. Measures are evaluated in context with qualitative program information and any documented justification. Moreover, severity of the errors or anomalies takes precedence over quantity because any error can potentially affect the reliability of the entire schedule network.
Table 11: Standard Data Measures for Schedule Best Practices
Measures in Best Practice 1 provide basic information on the scope of the schedule, such as number and types of activities and level of detail.
| Measure | Note |
|---|---|
| Total number of activities, including total summary, hammock, milestone, and detail activities | Summary activities may or may not be present in the scheduling software |
| Total number of remaining activities, including total summary, hammock, milestone, and detail activities | A remaining activity is any activity that is not complete. Remaining may be defined as (1) an activity with an actual start or no actual start and no actual finish or (2) any activity that is not 100 percent complete. Issues may arise with either definition. For instance, an activity may be noted as 100 percent complete and not have an actual finish date, or it may have actual start and finish dates but be less than 100 percent complete. Summary activities may or may not be present in the scheduling software |
| If applicable, number of activities marked as both a milestone and summary activity | An activity cannot be both a summary and a milestone |
| Number of activities with no descriptive name | May or may not be valid activities |
| Ratio of detail activities to milestones | Provides a rough indicator of the level of planning detail in the schedule. While there is no specific threshold, one or two detailed activities per milestone is probably a very low level of detail, while 10 is probably highly detailed |
| Number of activities not mapped to program or contractor work breakdown structure | |
| Number of contractor activities not mapped to a SOW paragraph or similar information | Depending on the nature of the effort, an activity may not be mapped to the statement of work |
| Number of activities with duplicate names | Activity names should be unique and descriptive |
Best Practice 2 includes more advanced measurements to assess the reliability of the network logic. Thresholds for measures are not provided because, in theory, any missing or inappropriate logic may disrupt the entire network. The assessment of this best practice is related to the assessment of Best Practices 5, 6, and 7. If major deficiencies are identified in Best Practice 2, then a valid critical path, total float, and horizontal traceability are not possible. For minor deficiencies, an assessment of the schedule’s critical path, total float, and response to tests of horizontal traceability are essential to understanding the implications of constraints and incorrect or missing logic. All activities in a schedule, regardless of detail or planning period, are subjected to this best practice.
| Measure | Note |
|---|---|
| Number of remaining detail activities and milestones missing predecessor links | Does not include the start milestone; missing links to external activities (activities outside the scope of the current schedule file) may be excluded when a schedule is evaluated outside the IMS network |
| Number of remaining detail activities and milestones missing successor links | Does not include the finish milestone; missing links to external activities (activities outside the scope of the current schedule file) may be excluded when a schedule is evaluated outside the IMS network |
| Number of remaining detail activities and milestones missing both predecessor and successor links | |
| Dangling activities: number of remaining detail activities and milestones with no predecessor on start date | Milestone activities may be excluded because their start and finish dates are the same; missing links to external activities (activities outside the scope of the current schedule file) may be excluded when a schedule is evaluated outside the IMS network; activities that have actually started may be excluded because their start dates have been determined |
| Dangling activities: number of remaining detail activities and milestones with no successor off finish date | Milestone activities may be excluded because their start and finish dates are the same; missing links to external activities (activities outside the scope of the current schedule file) may be excluded when a schedule is evaluated outside the IMS network |
| Percentage of logic links that are finish-to-start | The majority of relationships within a detailed schedule should be finish-to-start |
| Number of remaining detail activities and milestones with start-to-finish links | Count either successor or predecessor links but do not count both. An S-F link is between two activities but represents only one link |
| Number of remaining summary activities with logic links | May also be measured as “logic links to and from remaining summary activities”, although this may be a different number |
| Remaining detail activities and milestones with a great many predecessors | Assesses the schedule for path convergence. A relatively high number of predecessors may indicate a high-risk area. Note that not all predecessors are driving; only predecessors that have zero or low float have the ability to delay the successor when they are delayed |
| Remaining detail activities and milestones with soft date constraints | |
| Remaining detail activities and milestones with hard date constraints | |
| Remaining detail activities and milestones with active SNET date constraints | If an activity’s scheduled start date is the same as the SNET date, then the SNET constraint is more than likely preventing the activity from starting early. This is considered an active constraint. If an SNET constraint is earlier than the activity’s start date, then the activity is not affected by the constraint date |
| Remaining detail activities and milestones with active FNET date constraints | If an activity’s scheduled finish date is the same as the FNET date, then the FNET constraint is more than likely preventing the activity from finishing early. This is considered an active constraint. If an FNET constraint is earlier than the activity’s finish date, then the activity is not affected by the constraint date |
| Remaining detail activities and milestones with lags | Count either successor or predecessor lags but not both. A lag is between two activities but represents only one lag. This number is different from the number of lags |
| Number of lags on remaining detail activities and milestones | Count either successor or predecessor lags but not both. A lag is between two activities but represents only one lag. This number is different from the number of activities with lags |
| Remaining detail activities and milestones with leads | Count either successor or predecessor leads but not both. A lead is between two activities but represents only one lead. This number is different from the number of leads |
| Number of leads on remaining detail activities and milestones | Count either successor or predecessor leads but not both. A lead is between two activities but represents only one lead. This number is different from the number of activities with leads |
| Remaining detail activities and milestones with an F-S predecessor lead greater than remaining duration |
Best Practice 3 is more programmatic than quantitative, although measures and trends may be investigated for fully resource loaded schedules. If possible, resource assignments over time may be evaluated to identify potential unrealistic peaks. In general, the measures assess the number of activities within the detail planning period that are assigned resources and the reasonableness of work hours. Overallocated resources and unrealistic resource units should be a cause for concern. Care should be taken to assess only the appropriate detailed activities.
| Measure | Note |
|---|---|
| Total number of resources | |
| Overallocated resources | |
| Maximum units available per resource | Individuals should be available between 0 and 100 percent of full time, and resource groups should have a realistic number of individuals available to perform the work. |
| Summary activities and milestones with assignments | Summary activity durations depend on the activities contained within them. Milestones should never be assigned resources because they have no duration |
| Remaining detail activities with assignments | Exclude nonapplicable activities such as planning packages and reference activities |
| Remaining detail activities without assignments |
Measures for Best Practice 4 are generally straightforward, providing an overall assessment of the detail available to management, as well as the appropriateness of the schedule calendars. Care should be taken to assess only the appropriate detailed activities.
| Measure | Note |
|---|---|
| Remaining detail activities with dissimilar time units | All durations should be in the same unit, preferably days |
| Remaining detail activities or milestones starting or finishing on a weekend or holiday | May be legitimate but may stem from incorrect calendar assignments or specifications. Milestones on weekends or holidays should be questioned |
| Holidays and other exceptions by task calendar | |
| Remaining detail activities with durations less than the reporting period | Exclude nonapplicable activities such as planning packages and LOE and reference activities. The analyst should take into account baseline durations if available. That is, if the baseline duration is 35 days but the actual plus remaining duration is 60, the original baseline meets the intent of the best practice |
| Remaining detail activities with durations greater than the reporting period | |
| Average duration of remaining detail activities | |
| Median duration of remaining detail activities |
Best Practice 5 has no standard measurements. Vertical traceability is assessed by determining whether lower-level activities fall within the same time as higher-level activities and whether detailed schedule dates fall within the same time as summary schedule dates. An essential check of vertical traceability is determining whether forecasted milestone dates in detailed schedules match those quoted in management documents. Horizontal traceability depends on Best Practice 2, although not entirely as noted in that best practice. It is assessed by increasing activities’ durations by improbable amounts (500 or 1,000 days) and by observing how the schedule reacts. In the absence of constraints and assuming logic has been properly identified, key milestones should move and the critical path should change.
| Measure | Note |
|---|---|
| Assessment of how critical and noncritical planned dates dynamically react to dramatic increases in predecessor activity durations | Horizontal traceability implies that the network responds dynamically to delayed activities. Severely delayed activities should become critical and previously critical paths should become noncritical. Delays of this magnitude should cause the finish date to slip relative to the activity delay and reasonable available float |
Best Practice 6 has several standard measurements for assessing the validity of a critical path. Beginning at the program finish milestone, the sequence of driving activities is traced back to the status date. This sequence of activities should be straightforward, continuous, and the same as the critical path—defined by zero total float—in the absence of date constraints. Critical paths to interim key milestones may also be assessed as applicable.
| Measure | Note |
|---|---|
| Assessment of the driving paths to key milestones and comparison of those paths to activities marked as critical in the schedule | Ideally the longest path and critical path are the same to the key milestone. The path should be continuous from the status date to the key milestone |
| Number of critical activities | In general, if the ratio of critical path activities to the total remaining activity count is nearly 100 percent, then the schedule may be overly serial and resource limited |
| Number of critical LOE activities | A critical path cannot include LOE activities because they do not represent discrete effort |
| Number of lags and leads on the critical path | Lags cannot represent work and cannot be assigned resources |
| Number of critical activities with hard date constraints | Using hard constraints to fix activity dates at certain points in time immediately convolutes critical path calculations and defeats the purpose of CPM scheduling |
| Number of in-progress critical activities | Given that the critical path is a continuous sequence of activities from the status date, at least one in-progress activity is critical |
Best Practice 7 includes basic measurements of total float to assess overall program flexibility as reported by the schedule. It is closely related to assessments of Best Practices 2, 5, and 6, because a properly sequenced network produces reasonable estimates of float and a valid critical path. Reasonableness is assessed in combination with program length and activity type. In addition, because one logic error can cause an entire sequence of activities to report unreasonable amounts of float, the breadth of deficiencies reported in Best Practice 2 should be taken into account here. Negative float should always be questioned.
| Measure | Note |
|---|---|
| Remaining detail activities and milestones with dissimilar total float time units | All float should be in the same units, preferably days |
| Remaining detail activities and milestones with relatively high total float | High float is relative to the scope, length, and complexity of the schedule. Float should be reasonable and should realistically reflect the flexibility of the schedule |
| Remaining detail activities with negative total float | Negative total float indicates that the activity’s constraint date is earlier than its calculated late finish. Negative float may occur when activities are performed out of sequence |
| Average total float value of remaining detail activities and milestones | |
| Median total float value of remaining detail activities and milestones |
Many quantitative measurements are related to Best Practice 8, and a proper schedule risk analysis typically deserves a much more complex quantitative assessment than that given here. GAO’s assessment of Best Practice 8 is more programmatic, and these questions are provided in appendix II. The measures for Best Practice 8 are limited to determining the existence of risk data within the schedule risk file.
| Measure | Note |
|---|---|
| Fields within the schedule used for SRA | Fields that store optimistic, most likely, and pessimistic durations |
| Correlation measures within the schedule | |
| Contingency activities |
Best Practice 9 is assessed by determining the validity of the dates reported in the schedule. The assessment of this best practice depends on the status date reported in the schedule. It also depends on the scheduling software used: some software packages allow date anomalies that other software packages prevent.
| Measure | Note |
|---|---|
| Number of in-progress activities | An activity is in progress when it has started but is not yet complete |
| Number of remaining detail activities and milestones that have a forecasted start date in the past but no actual start date | Forecasted start dates should not occur in the past-i.e., any time preceding the status date |
| Number of remaining detail activities and milestones that have a forecasted finish date in the past but no actual finish date | Forecasted finish dates should not occur in the past-i.e., any time preceding the status date |
| Number of remaining detail activities and milestones that have an actual start date in the future | Actual start dates should not occur in the future-i.e., any time following the status date |
| Number of remaining detail activities and milestones that have an actual finish date in the future | Actual finish dates should not occur in the future-i.e., any time following the status date |
| Number of detail activities performed out of sequence |
Many data measures can be used to assess Best Practice 10; some are provided here. All baseline measures ultimately depend on the existence of a controlled baseline and a properly statused current schedule. Baseline measures are typically calculated by reporting period: for example, number of activities forecast to start early over the next 60 days or activities that have actually finished late over the past 6 months. They may also be useful when applied to specific products within the WBS, resource groups, or criticality: for example, the number of late activities during product integration, the average start variance of activities executed in one production plant, or the baseline execution index of activities with less than 10 days of total float.
| Measure | Note |
|---|---|
| Number of detail activities and milestones with baseline dates | Counts should accord with rolling wave planning periods |
| Number of detail activities and milestones without baseline dates | |
| Number of remaining detail activities and milestones that are forecast to start or finish before their baseline dates | Represents activities and milestones forecast to begin or end early |
| Number of remaining detail activities and milestones that are forecast to start or finish on their baseline dates | Represents activities and milestones forecast to begin or end on time |
| Number of remaining detail activities and milestones that are forecast to start or finish after their baseline dates | Represents activities and milestones forecast to begin or end late |
| Number of remaining detail activities that actually started before their baseline start date | Represents activities and milestones that actually started early |
| Number of remaining detail activities that actually started on their baseline start date | Represents activities and milestones that actually started on time |
| Number of remaining detail activities that actually started after their baseline start date | Represents activities and milestones that actually started late |
| Number of detail activities and milestones that actually finished before their baseline finish date | Represents activities and milestones that actually finished early |
| Number of detail activities and milestones that actually finished on their baseline finish date | Represents activities and milestones that actually finished on time |
| Number of detail activities and milestones that actually finished after their baseline finish date | Represents activities and milestones that have actually finished late |
| Average and median start variance | Start variance may be the difference between actual start and baseline start or forecast start and baseline start |
| Average and median finish variance | Finish variance may be the difference between actual finish and baseline finish or forecast finish and baseline finish |
| Baseline execution index | The ratio of actual completed detail activities to detail activities that were planned to finish. A BEI of 1 indicates that the project is performing according to plan. A BEI less than 1 indicates that, in general, fewer activities are being completed than planned; a BEI greater than 1 indicates that, in general, more activities are being completed than planned |
Source: GAO. | GAO-16-89G