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Coronavirus disease 2019 (COVID-19) changed the epidemiology of various diseases. The present study retrospectively investigates the epidemiologic and clinical changes in pediatric intussusception for ages ≤ 7 years before (February 2019–January 2020) and after (February 2020– January 2021) the COVID-19 outbreak in a single pediatric emergency department of a university-affiliated tertiary hospital. The incidence of communicable diseases—defined as infectious diseases with the potential for human-to-human transmission via all methods, non-communicable diseases, and intussusception were decreased following the COVID-19 outbreak (15,932 to 3880 (24.4%), 12,994 to 8050 (62.0%), and 87 to 27 (31.0%), respectively). The incidence of intussusception correlated significantly with the change in incidence of communicable diseases (Poisson log-linear regression, odds ratio = 2.15, 95% CI = 1.08–4.26, and p = 0.029). Compared with the pre-pandemic period, patients of the pandemic period showed higher proportions of pathologic leading point (PLP) and hospitalization (14.8% vs. 2.3% and 18.5% vs. 4.6%, respectively), lower base excesses (–4.8 mmol/L vs. –3.6 mmol/L), and higher lactate concentrations (1.7 mmol/L vs. 1.5 mmol/L). The incidence of pediatric intussusception decreased after the COVID-19 pandemic. This reduced incidence may be related to the reduced incidence of communicable diseases. However, the proportions of more severe diseases and PLPs were higher after the COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

The empirical studies on the Black-Scholes (B-S) option pricing model have reported that the model tends to exhibit systematic biases with respect to the exercise price, time to expiration, and the stock's volatility. This paper attempts to test the B-S model with a new approach: derive the confidence interval of the model call option value based on the confidence interval of the estimated variance. The test reports that even when the variance's confidence interval is considered, a systematic deviation between the theoretical "range" of the option price values and the observed market price still exist. If the stock variance is constant over time, the interpretation of the results is that the B-S model is wrong. However, if stock variance changes over time, the interpretation of the results is that the implied volatility in options market prices had a tendency to be significantly higher than the estimate that could have been obtained from historical data. [ABSTRACT FROM AUTHOR]