Total volume of stroke admissions per stroke service was not an independent predictor of mean thrombolysis rate nor of mean DNT. For the year of 2012 we also found no significant relationship between volume of stroke admissions and mean thrombolysis rates or mean DNT, when corrected for age, gender and type of hospital. There was a trend, towards higher thrombolysis rates in larger centers. When looking at the relationship between volume and DNT there seems to be a weak but significant relationship. Significance disappears when correction is used for age, gender and type of hospital. Interestingly, academic centers had higher thrombolysis rates, and lower DNTs together with non-academic referral centers, as compared to regional hospitals. So, even though there is a trend suggesting that larger volumes account for better results, this by no means reaches statistical significance, but organisational issues play a role in these process measures. This finding is in line with many previous studies showing no relationship between volume and processes or outcomes [
16,
17,
25]. In contrast, there have been studies that demonstrated a positive relationship [
26‐
28]. In general, these studies still lack to identify underlying reasons for higher thrombolysis rates and faster DNT in high volume hospitals. Other factors that might influence “in hospital” delay include transport between the emergency department to the CT scan laboratory or stroke department [
29]. One study found high volume hospitals to have fewer delays between arrival and brain scanning [
28]. Waiting for laboratory results, especially in patient using anticoagulants, has been reported as a delaying factor [
30]. Physicians are more cautious in using thrombolytic therapy in elderly patients [
25] patients with mild symptoms, or patients suffering from posterior circulation stroke [
30]. Several international studies suggest that thrombolysis in early arriving patients is due to be delayed by the thought that there is enough sufficient time before the time window ends [
25,
30]. The found differences between studies from different western countries is most likely due to different health care systems [
25,
28].
Most studies on the influence of stroke admission volume on outcomes of stroke care so far used threshold values in their statistical analysis [
13‐
17]. Generally, equal groups of high, medium and low hospitals are created. The cut-off values that are implied by this method have a direct influence on the conclusions [
16,
18,
19]. Besides this statistical flaw in using thresholds, they are clinically implausible as no sudden large improvement is expected when a hospital treats one patient more. There is no indication that one optimal threshold actually exists [
19]. To reliably assess the relationship between volume and outcome, we chose to analyse volume on a continuous scale.