Table 1.

Demographics and characteristics for the 48 study participants

Individual characteristics	N	Per cent
Male	48	100
Caucasian	42	88
Smoking status (current smoker)*	19	40
Other characteristics
Time of ECG (AM)†	18	38
Season of ECG (Winter)‡	33	69
Heart problems§	5	10
	Mean	SD
Age at start of study 2010 (years)	40	12
Number of years as a boilermakers (years)	9	9
Last weld day before study (days)	44	51

*Current smokers versus non-smokers and previous smokers.

†Morning (AM) versus afternoon (PM).

‡Winter versus summer.

§Heart problems include reported previous history of arrhythmia, cardiac sinus problems or palpitations.