Tehran University of Medical Sciences Nursing Practice Today 2383-1154 7 3 2020 07 01 161 162 Reza Negarande Nursing and Midwifery Care Research Center, School of Nursing and Midwifery, Tehran University of Medical Sciences, Tehran, Iran Raziyeh Beykmirza Nursing and Midwifery Care Research Center, School of Nursing and Midwifery, Tehran University of Medical Sciences, Tehran, Iran 2020 03 22 2020 03 22 The validity of the findings of the Systematic Review (SR) depends on the methodological quality of the individual studies in which they are included.  Therefore, evaluating the validity of the included studies is an integral component of a systematic review (1).  Bias or systematic error either exaggerates or underestimates the 'true' effect of an intervention or exposure. Typically, four sources for systematic error, including Selection bias, Performance bias, Attrition bias, and Detection bias, are considered in this assessment. https://npt.tums.ac.ir/index.php/npt/article/view/979 https://npt.tums.ac.ir/index.php/npt/article/download/979/446