Table 2. Effect of scan, patient and observer characteristics on agreement between observers and the reference standard.

Agreement on:	Acute Ischaemia		Rating point on 1/3 MCA scale
	Odds Ratio	p-value	Odds Ratio	p-value
Increasing hypoattenuation (3 point scale)	1.89	<0.0001	0.66	<0.0001
Increasing swelling (5 point scale	1.36	<0.0001	1.56	0.0001
Hyperattenuated artery (yes)	1.47	<0.0001	1.2	<0.0002
Old lesion present	1.33	<0.0001	0.94	0.028
Time to scan	1.13	<0.0001	1.19	<0.0001
Leukoaraiosis	0.59	<0.0001	1.85	<0.0001
Scan quality	1.04	0.3331	0.97	0.5007
Increasing age (effect per year)	1.01	0.0039	1.02	<0.0001
NIHSS	1.00	0.4804	0.99	0.0017
Neuroradiologists versus the rest	1.41	0.0025	1.34	0.0021
Read scan more slowly(per minute)	1.01	<0.0001	1.01	<0.0001
Years in training	0.99	0.1461	0.99	0.2943

An odds ratio of greater than one indicates increasing agreement and of less than one decreasing agreement with the reference standard reader on the presence of acute ischaemia or the rating point on the 1/3 MCA scale (note the pattern was similar for all three scales therefore only 1/3 MCA scale shown).

MCA  =  middle cerebral artery; NIHSS  =  National Institutes of Health Stroke Scale.