Correlation between breast cancer and lifestyle within the Gulf Cooperation Council countries: A systematic review

Table 9 Critical appraisal of case-controlled studies using National Institutes of health study quality checklists

Critical assessment of case-controlled studies
	Al-Amri et al[40], 2015	AlFaris et al[41], 2018	Alothaimeen et al[61], 2004	Elkum et al[39], 2014
Was the research question or objective clearly stated?	Y	Y	Y	Y
Was the study population clearly specified and defined?	Y	Y	Y	Y
Did the authors include a sample size justification?	Y	N	Y	N
Were controls selected or recruited from the same or similar population that gave rise to the cases?	Y	Y	Y	Y
Were the definitions, inclusion and exclusion criteria, algorithms or processes used to identify or select cases and controls valid, reliable and implemented consistently across all study participants?	Y	Y	N	Y
Were the cases clearly defined and differentiated from controls?	Y	Y	Y	Y
If less than 100% of eligible cases/controls were selected for the study, were the cases/controls randomly selected from those eligible?	NA	NA	NA	Y
Was there use of concurrent controls?	N	N	N	Y
Were the investigators able to confirm that the exposure/risk occurred prior to the development of the condition or event that defined a participant as a case?	Y	N	CD	N
Were the measures of exposure/risk clearly defined, valid, reliable and implemented consistently across all the study participants?	N	Y	y	Y
Were the assessors of exposure/risk blinded to the case to the case or control status of participants?	Y	N	N	Y
Were key potential confounding variables measured and adjusted statistically in the analyses? If matching was used, did the investigators account for matching during study analysis?	Y	N	Y	Y
Quality rating	Poor	Poor	Poor	Good
Additional comments	Controls not well defined and were not concurrent	High risk of bias and confounding not adjusted for	Cases were significantly older than the controls (P = 0.0001). High risk of bias

Available online at https://www.nhlbi.nih.gov/health-topics/study-quality-assessment-tools. Y: Yes; N: No; CD: Cannot determine; NA: Not applicable; NR: Not reported.