5.70. The level of detail to which the model is developed and the associated amount and quality of data necessary will depend on the context for the assessment (see Section 4). For example, in early versions of the safety case (such as site selection or initial investigations), it might be sufficient to generate relatively simple models for screening purposes that can be implemented using simple computer tools such as spreadsheets and data that are readily available. Following the review of the results, it might be appropriate to improve certain models and collect further data, and to implement them using more sophisticated computer codes. Models and data for later revisions of the safety case, especially for the final revision, may need to be even more comprehensive.