Program Evaluation and Review Technique

A project management tool, which is represented by a flow chart, used to estimate and analyse activity timings, which are estimates in weeks or fractions of weeks, to complete tasks within a project, along with any dependencies of activities on others being completed beforehand, ultimately helping to identify the critical pathway to achieving the desired outcome. PERT can be useful where times of activities are not known, or poorly understood, or potentially quite variable due to different equipment and / or staff capabilities. It can also be more useful where experimentation of activities is being carried out and deadlines aren’t as time critical as for contractual projects, or similar.

The flow chart consists of arrows which represent the activities being undertaken, and nodes which represents the event of having achieved a milestone. Several activities can be taking place at the same time, although some subsequent activities will typically have to wait until one or more activities have been completed before work can proceed further. Where the technique is being used for activities that individually might be inconvenient to measure in fractions of weeks, then the use of hours of fractions of days might be considered as a variation on the traditional approach. This might be more suitable for grounds management programmes.

The main limitation of the PERT technique is that it “only deals with the time constraint and does not include the quantity, quality, and cost information desired in many projects…”, (Evarts, H.F. (1966) ‘Introduction to PERT’, p.4). As an estimate for time-scheduling then this technique can be useful, but more so as a complement to other techniques, for example Gantt Charts and Critical Path Analysis.

Estimating times to complete an activity involves the use of an aggregating formula which looks at different potential times: the most likely time (MLT) to complete the activity, an optimistic time (OT), which is the quickest time if everything was ideal situation, which is unlikely in practice, and a pessimistic time (PT), which is the longest time if everything doesn’t go to plan, again which is unlikely in practice. This will then help produce the expected time (ET), which is the best calculated estimate of how long the activity will take for project planning purposes. A couple of constants are also included in the formula that aim to create a more realistic project time from the variable times that might be included. The sum total of the individual activities is calculated to identify the estimated time to achieve the event / milestone.

Expected time per individual activity = (OT + 4(MLT) + PT) ÷ 6

An annual football pitch maintenance programme might be an example of a project for which a PERT can be use, especially where volunteers are maintaining a pitch as their timings will typically be more variable than full-time employed professionals. With the outcomes not being as time critical as for example that which would be needed for professional league football pitch maintenance then this approach can help give a useful guide.

Whilst work activities aren’t repetitive (if this is interpreted as being the same day-in and day-out), some activities are undertaken frequently throughout the year, although environmental conditions will influence the actual time taken, so having an expected time made up from the different estimates can be a useful guide for overall annual inputs helping to identify adequate staffing levels.

Correct sequencing of activities is essential in grounds maintenance if effective use of resources is to be achieved, so, for example, if planning renovation activities the overseeding and fertiliser application wouldn’t be carried out before initial preparation of the sward has taken place, with might be heavy scarification, cultivation by power harrow, or a fraise activity, or similar. The application of a top-dressing would clearly take place after preparation as well.

An example of an expected time might be the following: Fertilise the pitch by pedestrian broadcast spreading equipment.

• Optimistic time = 60 minutes
• Pessimistic time = 180 minutes
• Most likely time = 100 minutes

Expected time (for project purposes) = (60 + 4(100) + 180) ÷ 6 = 107 minutes. Whilst the result in this example is only 2.5% less than the ‘most likely time’, it wouldn’t really have much use in practice for short projects, however, as previously mentioned, the timings calculations might be more suitable for annual maintenance programmes and it might be appropriate to typically be rounded up to a more uniform figure of 2 hours or ¼ of a day in this instance.