This paper presents an extended version of Goal-Oriented Requirements Analysis Method called AGORA, where attribute values, e.g. contribution values and preference matrices, are added to goal graphs. An analyst attaches contribution values and preference values to edges and nodes of a goal graph respectively during the process for refining and decomposing the goals. The contribution value of an edge stands for the degree of the contribution of the sub-goal to the achievement of its parent goal, while the preference matrix of a goal represents the preference of the goal for each stakeholder. These values can help an analyst to choose and adopt a goal from the alternatives of the goals, to recognize the conflicts among the goals, and to analyze the impact of requirements changes. Furthermore the values on a goal graph and its structural characteristics allow the analyst to estimate the quality of the resulting requirements specification, such as correctness, unambiguity, completeness etc. The estimated quality values can suggest to him which goals should be improved and/or refined. In addition, we have applied AGORA to a user account system and assessed it.