Table. Levels of expired carbon monoxide in non-smoking waiters and medical students.

Subjects	Median carbon monoxide - ppm (interquartile range)
Medical Students (n = 100)	2.5 (1.0 to 4.0)
Waiters: pre-exposure (n = 100)	2.0 (1.0 to 3.0)†
Waiters: post-exposure (n = 100)	5.0 (3.0 to 8.0)*

ppm = parts per million

^†= Mann-Whitney test showing homogeneity of medical students’ and waiters’ pre-exposure carbon monoxide levels, P = 0.18

^*= Wilcoxon test comparing waiters’ pre- and post-exposure carbon monoxide levels, P < 0.001.