Abstract: Objective To explore the processing Methods of big data of hospital information systems(HIS) and analyze the characteristics and trends of outpatient visits and medical services in a tertiary pediatric hospital in Shanghai during the past 10 years.Methods Data were extracted from the database of outpatient registry in HIS from 2009 to 2018. Data cleaning (diagnosis, address, replication, outliers, and missing data), data assembly (linkage of database), data reduction, data anonymization and data audit were conducted according to the procedure of big data. We analyzed the characteristics and trends of outpatient visits and medical services.Results The total outpatient visits from 2009 to 2018 were 20,775,899 and 18,242,822 visits were included in this study. Males were 4,656,843 accounting for 57.42%. Patients under 1 year old, from 1 to 3 years old, from 3 to 7 years old and from 7 to 18 years accounted for 9.57%,40.94%, 24.82% and 24.67% respectively. The missing data rate of diagnosis, address, and name of doctors was 5.92%, 45.31% and 28.61%,respectively. There were no significant differences in the percentage of sex and age in different years among the population with missing data. The average increasing rate of outpatient visits was 5.22% in the past 10 years. The increasing rate of 2012 and 2014 were 11.22% and 10.93% respectively, compared with the same period of last year. The increasing rate slowed down to 2.90% after 2015. The distribution of outpatient address showed the trends of expansion from the east of China to the South-west, North-west, South, Middle and North-east. The average workload of a doctor was 51 visits in a day. According to professional titles, there were 63, 54, and 45 visits per day for junior, intermediate, and senior doctors, respectively. The number of specialty clinics increased from 46 in 2009 to 180 in 2018 and serviced the 68.12% of outpatient visits. The number of specific disease clinics increased from 16 in 2009 to 142 in 2018.Conclusion The big data of outpatient visits in a tertiary pediatric hospital(National Children's Medical Center) in China showed that there was a sustainable upward trend in outpatient visits; the origin of patients expanded from Shanghai to the whole of China; the average visits for a single physician were lower than that of the country. Specialized clinics in specialties or diseases are an important trends for the development of children's hospitals.

Key words: Hospital information system, Outpatient, Pediatrics, Specialty clinic, Specific disease clinic, Workload