We will search Pubmed ("Systematic Review"[Title/Abstract] OR "meta-analysis"[Title/Abstract] OR "metanalysis"[Title/Abstract] OR "meta analysis"[Title/Abstract]) AND ((y_1[Filter]) AND (fft[Filter]) AND (english[Filter])) AND (systematic [sb]) and will include he following types of Systematic Reviews (SR) with or without meta-analysis, in medical research: Association: including SR of association and risk; Proportion: including SR of prevalence and incidence; Descriptive: including SR of phenomenon, case reports, case series and surveys. The above mentioned classification is based on the report Munn et al.