Text and Data Mining valid from 2019-11-05
First Online: 5 November 2019
Compliance with Ethical Standards
: The authors declare that they have no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of Yonsei University, the Center for Research Ethics Information in Korea, and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.
: Mothers and teachers were provided with written information about the study and informed consent was obtained from all individual participants included in the study before the survey started.