Table 2:

Outcome of repeat examination by interval since the examination with negative findings^{^a}

Interval between CTs	No. of Positive Examinations	Total Repeat Examinations	% Positive	P Value^{^b}
<30 days	5	344	1.5	.011
<60 days	8	491	1.8	.007
<90 days	9	605	1.7	.002
<120 days	10	690	1.6	<.001
<180 days	11	804	1.5	<.001
>180 days	25	1359	1.8	<.001

↵a Outcome of repeat NCHCT examinations as a function of the interval (in days) since the prior examination with negative findings. The proportion of repeat examinations with positive findings remained between 1.5% and 1.8% (and significantly lower than the 4.3% positive rate of first/baseline examinations) for the durations (up to 1 year) considered in this study.
↵b The P value was taken against the 4.3% rate of first/baseline examinations.