How do you think the confidence interval was presented in the study was calculated? Explain the mathematical concepts could you extract from this article

I chose an article that was published in the Journal of Anesthesia and Analgesia about trends in Postpartum Hemorrhage. Postpartum Hemorrhage is excess bleeding after childbirth and can be caused by many different factors. The article describes PPH as the leading cause of morbidity and mortality in the United States. The frequency of PPh increased during the 1990s and 2000s. The Purpose of the study was to reevaluate trends in PPH using the National Inpatient Sample. Data showed an increased from 2.9% (95% confidence interval [CI], 2.7% 3.1%) to 3.2% (95% Cl, 3.1%- 3.3%) of deliveries. The sample size and confidence level were both used and listed in the article which is stated above including the confidence interval of 95% The confidence interval in this article refers to the estimate of patients who are at risk for PPH. Reference: Reale, Sharon C. MD; Easter, Sarah R. MD; Xu, Xinling Ph.D.; Bateman, Brian T. MD, MSc; Farber, Michaela K. MD. MS. Trend in Postpartum Hemorrhage in the United States for 2010 to 2014. https://journals.lww.com e