Definition of shifts and stratification. Shifts were generally defined using patterns of time of day of TC observed in data obtained by a cross-sectional study described elsewhere [36]. All non-fatal TC victims, who had suffered TC and attended the two Porto Alegre emergency rooms during the 45 days of data collection, answered a structured interview, and were then breathalysed. Frequencies of alcohol related TC were tabulated according to the weekday and 3-hour period of the day, such as 0-3am, 3am–6am, etc. initially aiming to define four ‘‘six hour’’ shifts. The first (=1.59) and third (=4.76) quartiles of the alcohol–related TC distribution were used as cut-off points to define the three strata: (1) low prevalence (#1.59; not highlighted in Table 1); (2) intermediate prevalence (.1.59 and #4.76; with italics in Table 1); and (3) high prevalence (.4.76; with bold in Table 1).