project management
05.06.2024
Effective time and resource planning using the PERT method
Lucas Falkowsky
Fullstack Development
The be-all and end-all for a successful sprint or project completion is to carry out the most accurate and professional effort estimation possible at the beginning. This is where the PERT method comes in.
<p>Das A und O für einen erfolgreichen Sprint- oder Projektabschluss ist es, zu Beginn eine möglichst akkurate und professionelle Aufwandschätzung durchzuführen.</p>
<p>Bei Projektplanungen stehen Führungskräfte häufig vor der Herausforderung, dass aufgrund unvorhergesehener Komplexität oder ungenügender Weitsicht Fehlprognosen und dadurch Fehlkalkulationen zustande kommen. Fehlkalkulationen, die zu schweren Folgen für das Unternehmen führen können, wie unzufriedene Kunden, finanzielle Engpässe, aber auch überlastete Mitarbeiter:innen, die unter Stress ihr volles Potential nicht ausschöpfen können.</p>
<p>Im Folgenden geben wir einen Einblick, wie Kapazitäten im Zuge eines gut organisierten Critical-Chain-Managements mit Hilfe von modernen Methoden besser eingeplant werden können und wie Prognosen über die aufzuwendende Zeit, und dadurch finanzielle Ressourcen, zuverlässiger durchgeführt werden können.</p>
<h2>Aufwandsschätzungen mit der PERT-Methode</h2>
<p>Die PERT-Methode, auch bekannt als <strong>P</strong>rogram <strong>E</strong>valuation and <strong>R</strong>eview<strong> T</strong>echnique, wurde in den 1950er Jahren entwickelt und dient seither vielen Unternehmen als eine zuverlässige Methode zur Schätzung von Arbeitsaufwand. Die PERT-Methode basiert auf der Annahme, dass Aufwandsschätzungen mit Unsicherheiten behaftet sind und verschiedene Szenarien berücksichtigt werden müssen.</p>
<p><img src="https://typedig.uber.space/assets/4d0d01a8-d109-46ae-bbc9-ac479d5c62c2?width=1440&height=1920" alt="Typedigital Zunder Foto 20230628 94"></p>
<p><em>Thanks to the application of the PERT method, we are able to estimate projects with a remarkably high degree of accuracy.</em></p>
<p><em>Thanks to the application of the PERT method, we are able to estimate projects with a remarkably high degree of accuracy.</em></p>
<h2>PERT method: procedure and examples</h2>
<p>When using the PERT method, the estimate is first divided into three categories: <em>optimistic, pessimistic</em> and <em>probable</em>.</p>
<p>Two examples illustrate this categorisation:</p>
<p>1st example - a situation familiar to everyone: getting to an important meeting in another city on time.</p>
<p>Optimistic estimation: <em>problem-free use of transport, green traffic light phases, minimum transfer time for a connecting train, no hurdles on the way and no additional parameters that hinder the destination are estimated. The smallest possible time budget is assumed here and the meeting could start at 08:00 sharp.</em></p>
<p>Pessimistic estimate: <em>Problems are planned for, such as a possible strike, delays due to roadworks, missed connections, etc. The time budget is open-ended and the pessimistic estimate means that the meeting may not start until 11:00.</em></p>
<p>Probable estimate: <em>Based on experience, a connection is sought where the transfer time of the connecting train allows sufficient time. In this case, the meeting could be scheduled for 09:00.</em></p>
<p>Zwei Beispiele veranschaulichen diese Kategorisierung:</p>
<p>1. Beispiel - eine Situation, die jeder kennt: pünktlich zu einem wichtigen Termin in einer anderen Stadt zu kommen.</p>
<p>Optimistische Schätzung: problemlose Nutzung der Verkehrsmittel, grüne Ampelphasen, minimale Umsteigezeit für einen Anschlusszug, keine Hürden auf dem Weg und keine zusätzlichen Parameter, die das Ziel behindern, werden geschätzt. Hier wird das kleinstmögliche Zeitbudget angenommen und das Treffen könnte um Punkt 08:00 Uhr beginnen.</p>
<p>Pessimistische Schätzung: Es werden Probleme eingeplant, wie z. B. ein möglicher Streik, Verspätungen aufgrund von Baustellen, verpasste Anschlüsse usw. Das Zeitbudget ist offen und die pessimistische Schätzung bedeutet, dass die Besprechung möglicherweise erst um 11:00 Uhr beginnt.</p>
<p>Wahrscheinliche Schätzung: Erfahrungsgemäß wird eine Verbindung gesucht, bei der die Umsteigezeit des Anschlusszuges ausreichend Zeit lässt. In diesem Fall könnte das Treffen für 09:00 Uhr angesetzt werden.</p>
<h3>Use of statistical methods to calculate the average time</h3>
<p>In the next step, the time estimates are combined with statistical methods in order to obtain a realistic forecast. This is where the so-called beta distribution is used, which makes it possible to calculate the probability of the various scenarios. The PERT method uses these probabilities to determine a weighted average time.</p>
<p>The beta distribution is relevant because, on the one hand, an internal company target is estimated and, on the other hand, a target is communicated externally. </p>
<p>Example 1: Reaching an important meeting in another city on time.</p>
<p>Based on my optimistic, pessimistic and probable estimates, I assume a journey time of two hours. To avoid being late for a meeting, I let them know that the meeting will take place at 09:45. By making this appointment, I prevent myself from being late and people having to wait for me. The 45 minutes added to the optimistic value correspond to an additional standard deviation from my probable estimated value. This means that I have a high probability of being almost 100% on time for the meeting and my colleagues are spared unnecessary delays.</p>
<p><strong>2nd example: Integration of an API</strong></p>
<p>My team colleagues need the API data to be able to work on other tickets. If too little time was scheduled during the estimation, this quickly leads to blockers within the team. The other people cannot work as long as the API data is not usable. For this reason, an additional standard deviation value is estimated to prevent resources from being involved too early.</p>
<h3>Consideration of dependencies: Critical chain management</h3>
<p>Another important aspect of the PERT method is the consideration of dependencies between processes or tasks, known as critical chain management. This is done with the help of a whiteboard that visualises the relationships between the tasks. In this way, the critical path can be determined and bottlenecks in the progress of the project can be identified.</p>
<p><img src="https://typedig.uber.space/assets/5e650d05-318e-4044-892a-c297c7d47987?width=1440&height=1920" alt="Typedigital Zunder Foto 20230628 46"></p>
<p><em>Dependencies between tasks and processes are captured using visualisations</em></p>
<p><strong>Example 1: Reaching a meeting in another city</strong></p>
<p><em>The route to the first bus stop is not influenced by any other factors. Here I am free and can simply walk to the bus stop.</em></p>
<p><em>What is influenced are the processes that depend on my punctuality: If I'm late, the meeting won't take place on time. All participants with follow-up appointments therefore have to reschedule or cancel meetings.</em></p>
<p><em>I estimate the start of the journey and the meeting time. The two estimates are interdependent.</em></p>
<p><em>All processes that need to take place in order to reach the meeting in the other city on time depend on the punctuality of the first connection (the bus).</em></p>
<p><strong>2nd example: Integration of an API</strong></p>
<p><em>Let's assume that I am implementing an API. My colleague is supposed to work on it a week later. She will need the data from the API to finalise other tickets. If I don't manage to integrate the API after the estimated working time, I will block my colleague, which will lead to idle time. It is therefore essential to plan a standard deviation that extends the processing time (buffer). This means I have a realistic time frame available and blockages can be avoided.</em></p>
<p><strong>Conclusion</strong></p>
<p>Accurate effort estimates are essential in agile management to ensure successful project completion. The PERT method is a proven tool for this, as it takes optimistic, pessimistic and probable scenarios into account. In combination with statistical methods and the consideration of dependencies, effective time and resource management can be guaranteed.</p>
<h3>Benefit from our knowledge of the PERT method</h3>
<p>As experienced experts in digital product development, we help companies with strategic planning and the successful implementation of complex digital projects. In doing so, we not only serve as implementers, but also provide support through partnership-based consulting on topics such as agile management. Contact us today to find out how we can best support you in your project plans. We look forward to hearing from you.</p>
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