The changing trends in attendance rates were estimated by calculating the difference between base year and last year.

An average signal was analysed for each of 120 possible BLs obtained by calculating the difference between pairs of unipolar leads.

Interobserver reproducibility was assessed by calculating the difference between measurements taken by the two operators (limits of agreement) and interclass correlation coefficient.

Intraobserver repeatability was assessed by calculating the difference between two measurements for each variable (limits of agreement) and further expressed as an intraclass correlation coefficient.