A concern that has a probability of occurrence equal to one, a consequence of occurrence greater than zero, and a time-frame that is current. A problem is an event that has occurred and has a negative impact to the project. (Conrow 2008)
Conrow, E. 2008. "Risk Analysis for Space Systems". Space Systems Engineering and Risk Management Symposium, 27-29 February, 2008, Los Angeles, CA, USA.
Defines problem in terms of probablity of occurrence, consequence of occurrence, and time-frame; all of which are measurable.