Complex sentence: By 2006, the total number had risen to over 700,000 but when adjusted for population changes, the tonsillectomy "rate" had dropped from 0.62 per thousand children to 0.53 per thousand.
Split into simpler sentences: By 2006, the total number had risen to over 700,000. However, when adjusted for population changes, the tonsillectomy "rate" dropped from 0.62 per thousand children to 0.53 per thousand.