what is the monthly average protein/creatinine ratio level of patient 88401 last year?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 88401 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'protein/creatinine ratio' ) and datetime(labevents.charttime,'start of year') = datetime(current_time,'start of year','-1 year') group by strftime('%y-%m',labevents.charttime)