Competence-based estimation of activity duration in IT projects

Highlights

• A proposed algorithm for the estimation of IT project activity duration.

• The algorithm relies on a hierarchical skill model and learning curves.

• Interrelated skills are taken into account.

Abstract

The aim of project management is to successfully complete the project on schedule and within budget. Estimation of project activity duration is a key feature of scheduling. The individual activities making up the schedule and the estimation of their duration are crucial for defining the project timetable. The resulting scheduling problem falls into the class of Multi-Skill Resource-Constrained Project Scheduling Problems. In this paper we propose a novel methodology for Activity Duration Estimation in IT projects. The methodology uses the Hierarchical Skill Model and takes into account the experience of project team members, described by required and possessed skills. Skills are modeled as a weighted digraph, and learning curves are used to express individual learning rates. An illustrative example using a software project is provided. Incorporating skill-based modeling into project scheduling results in more precise estimation of actual and future performance.

Introduction

In the lifecycle of a software project, after finishing the requirements-gathering phase and before the development phase, there is a time for planning the project: resources, schedule, budget and risks. In this paper we focus on constructing the project schedule and particularly on the estimation of activity duration. According to PMBOK (2009), an activity is a component of work performed during the course of a project. In project management an activity is the smallest unit of work, described by four parameters: resource consumption, logic relationships with other activities in the project, associated cost, and duration. Activities are the building blocks of a project. Work Breakdown Structure (WBS) at the lowest level of detail of work packages. An activity is a work package that: (1) makes no sense to break down any further, (2) produces a deliverable which is measurable (3) endures no longer than a single reporting period and (4) has a duration that can be realistically estimated. Duration here is defined as the period of time required for completion of an activity, excluding non-working hours.

Activity duration can be estimated by several methods: analogy, expert judgement, parametric or WBS. Estimation by analogy is based on a comparison of the effort and time taken to complete previous similar tasks (Morgenshtern, Raz, & Dvir, 2007). Project managers study the similarities between the two activities and adjust for any features that may result in differences in duration. In this adjustment lies the difficulty of this low-cost technique. Expert judgment involves using specialists who have experience in estimating activity duration and knowledge of the particular field. Hughes (1996) shows that expert estimation can be reasonably accurate. The drawback of this method is that it is hard to separate expert subjectivity from experience and to identify the factors contributing to the estimation. Parametric estimation is based on formal models that take into account various factors affecting time and effort. For instance in the Function Points method the number of entities and their complexity is calculated. The WBS method estimates time and effort by hierarchical decomposition of a project into smaller units; the smallest units are activities. The COCOMO method (Boehm, 1981) defines a project by the program size (number of lines of code). A project is classified as organic, semi-detached or embedded; based on this division, appropriate weights are assigned. The methodology was further developed into COCOMO II (Boehm et al., 2000), which defines six personnel-related attributes: Analyst Capability (ACAP), Programmer Capability (PCAP), Personnel Continuity (PCON), Applications Experience (APEX), Platform Experience and Language (PLEX), and Tool Experience (LTEX) (Lum et al., 2003). All six are defined at five proficiency levels, which describe the capability and experience of personnel, assigned to the project.

In all these methods the estimation of activity duration is performed for a typical (average) or the best (most experienced) team member. Only in COCOMO methods are these estimates modified, using predefined weights, to take personnel factors into account. In the manufacturing industry, a well-known approach to workforce performance assessment is the use of learning curves, introduced by Wright in 1931. The foundation of this approach is the assumption that employee productivity increases as a function of the number of repetitions or of the time spent on a particular task. This can be applied to a project where operations executed within activities are repetitive, i.e., one can gain experience in executing them, which finally manifests as shortened activity completion time. It has also been shown that work can be characterized by required competences, i.e., the arbitrarily defined human factor affecting organizational performance (Boucher, Bonjour, & Grabot, 2007). ISO 9001 (2008) defines ‘competence’ as “the ability to apply knowledge and skills to achieve intended results”.

In this paper we propose a novel approach to the estimation of IT project activity duration that takes into account the skills required to perform an activity and the project team members’ experience in using these skills. Our methodology allows a more precise prediction of activity duration and required team member experience. The initial duration is the time that would be required by a very experienced team member; this is then adjusted according to the capabilities of a less experienced team member, for input to a resource-scheduling algorithm. Moreover, our methodology takes into account that team members are multi-skilled, and that experience gained as a result of performing one activity improves performance in a different but similar activity. The similarity here is characterized with use of a Hierarchical Skill Model (Małachowski & Korytkowski, 2016).

Describing team members’ competences will also allow us to keep track of employee competence levels so that persons can be assigned to project activities more efficiently. This approach enables better career path planning and progress monitoring, and more effective motivation.

The paper is organized as follows. The next section summarizes relevant literature on estimation methods of project activity duration in resource-constrained project scheduling, learning curves and skills modeling. In the third section, an MSPCP model with learning curve and interrelated skills is described. In the fourth section, an Activity Duration Estimation algorithm is presented. The fifth section describes a case study of an IT project development. Our conclusions and recommendations are presented in the final section.