Tabriz University of Medical Sciences Journal of Cardiovascular and Thoracic Research 2008-5117 11 1 2019 03 16 Considering the design effect in cluster sampling 78 78 10.15171/jcvtr.2019.14 EN Yousef Alimohamadi https://orcid.org/0000-0002-4480-9827 Mojtaba Sepandi LETTER 10.15171/jcvtr.2019.14 2018 10 11 2019 02 11