“…Many studies have used CO 2 as a marker for exposure levels indoors and for ventilation efficiency, and examined the relationship between measured concentrations of CO 2 and subjectively assessed acute health symptoms (e.g., Seppänen et al, 1999;Apte et al, 2000;Erdmann et al, 2002), impairment in cognitive performance (e.g., Myhrvold et al, 1996;Myhrvold and Olesen, 1997;Coley et al, 2004;Bakó-Biró et al, 2008;Haverinen-Shaughnessy et al, 2011;Wargocki and Wyon, 2013) and absence rates (e.g., Milton et al, 2000;Mendell et al, 2013). In all of these studies, none of the observed effects were attributed to CO 2 .…”