Box 2.

Service change classification

For April and September: no change: activity remained within 15% of the baseline level; increase: an increase of >15% from baseline; small drop: a reduction of between 15% and 60% from baseline; large drop: a reduction of >60% from baseline. Overall classification: no change: no change in both April and September; increase: an increase in either April or September; sustained drop: a small or large drop in April, which has not returned to within 15% of baseline by September 2020; recovery: a small or large drop in April, which returned to within 15% of baseline (‘no change’) by September 2020.