Is the curve relating temperature to aggression linear or curvilinear? Assaults and temperature in Minneapolis reexamined

Using archival data from Minneapolis recorded in 3-hr time intervals, E. G. Cohn and J. Rotton (1997) concluded that there is an inverted U-shaped relationship between temperature and assault, with the maximum assault rate occurring at 74.9 F. They depicted this relationship by plotting temperature against assault. This plot, however, fails to take into account time of day. Time of day was strongly related to both temperature and assault, but in opposite directions. Between 9:00 p.m. and 2:59 a.m. of the next day, when most assaults occurred, there was a positive linear relationship between temperature and assault. The Minneapolis data actually provide stronger support of a positive linear (or monotonic) relationship between temperature and assault than of an inverted U-shaped relationship.