My PhD is examining nursing complexity in hospital ward systems. Nurses simultaneously care for many patient sharing place and time. Many patient situations and events that the nurse has to deal with will arise at precisely the same moment in time. Complexity arising from simultaneously arising events in time has been labelled 'combinatorial complexity.' The greater the number of patients a nurse is responsible for in time and place the greater the probability that combinatorial events will occur. Is it possible to express the probability of simultaneous events occurring in populations of patients sharing place and time? These simultaneous occurring events only matter to nurses because they have to deal with each event in linear time which delays others care.