## 3 The Early Phase Project Scope Estimation Methodology
### Scope Estimation  
After collecting and reconciling the requirements, the project scope estimation is performed (step S5 in Figure 2), which encompasses defining the priorities and level of clarity, evaluating the story points, and calculating the estimate for each requirement. This is performed by reaching a group consensus, according to the story point estimation principles [37].  
Prioritization is an optional step, but it can be useful for calculating the scope of various requirement sets, grouped by priority. Depending on the information available, priorities can be obtained from the source models or introduced manually. If necessary (or when the team decides to do so), the priority of the requirement can be adjusted, or the requirement can be removed from the scope assessment. This is the initial prioritization. More detailed prioritization is performed later during the development process.  
Additionally, a level of clarity is identified for each requirement. We suggest using four levels of clarity (although these levels can be modified according to the specifics of the project and the team):  
* Level 1 (the requirement is very clear, and its purpose is understandable);
* Level 2 (the requirement raises questions and is not completely clear);
* Level 3 (the requirement has several solution options, it is not clear which way it will have to be carried out);
* Level 4 (the requirement is not clear, which raises many questions that will be answered after additional analysis or implementation of other functionalities).  
The coefficient of clarity for each level can be custom; we suggest using 1 for level 1, 1.3 for level 2, 1.5 for level 3, and 2 for level 4. The coefficient of clarity increases the amount of work that will potentially be required for the requirement.  
The next step is using expert judgement to assess the scope of each requirement in story points according to Agile estimation principles [37]. If the scope of the requirement is very small, the requirement can be merged with other requirements to make the list clearer and easier to control. If the scope of the requirement is very large, it should be broken down to make its components clearer. After assessing all requirements, the scope can be estimated for each requirement according to the following formula:  
\[\textit{Requirement\;Scope}=\textit{Requirement\;Story\;Points}^{*}\textit{ Coefficient\;of\;Clarity} \tag{1}\]  
The distribution of requirements according to the assigned level of clarity and the number of story points assessed is a good indicator of the quality of the results of requirements elicitation. If the requirements are mostly evaluated in 3-8 story points and assigned level 1 or level 2 coefficients of clarity, it can be concluded that a manageable list of requirements is obtained, and it can be used in the next steps of the project. In the opposite case of the predominance, i.e., when requirements are evaluated in 13 and more story points are level 3 or level 4, coefficients of clarity prevail. In this case, it is necessary to either repeat the workshop or offer the client an additional requirements discovery phase, during which the requirements would be detailed, and their complexity and level of uncertainty would be reduced. The level of clarity of each requirement group (if requirement grouping is used) is also important. This helps to understand whether it will be possible to start development as soon as the project starts or if it is needed to pay more attention to the analysis. If there are no requirement groups where the clarity is good (level 1 or level 2), then the start of the project will be complicated, with limitations in parallel implementation of several parts of the system under development.  
Finally, the estimate of all project scope is acquired by summing up all calculated requirements scopes. Other strategies for estimation can also be used, e.g., including only requirements with high and very high priorities in project scope estimation.