Forensic scientists lack a uniform system and common vocabulary for presenting conclusions about the sources of the traces or the weight of the evidence associated with these traces. Practices vary both across fields and sometimes within them. Several modes of presentation coexist, such as categorical conclusions (e.g. 'the trace has been identified as coming from Mr. X'), or less definitive but easily misunderstood observations (such as 'the trace is consistent with coming from Mr. X' or 'the trace matches Mr. X'). In some fields, practitioners qualify their conclusions about the identity of sources with verbal probabilities (such as 'there is a strong probability than Mr. X left the trace').