what is the average total cost of the hospital, which includes the pressure ulcer, stage iv this year?
select avg(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select diagnoses_icd.hadm_id from diagnoses_icd where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'pressure ulcer, stage iv' ) ) and datetime(cost.chargetime,'start of year') = datetime(current_time,'start of year','-0 year') group by cost.hadm_id ) as t1