title: Validity and reliability.
authors.affiliation: Department of Community Health Sciences, Aga Khan University, Karachi.
authors.forename: M M
authors.initials: MM
authors.lastname: Kadir
authors.forename: A F
authors.initials: AF
authors.lastname: Qureshi
mesh_terms: D015982:Bias; D015986:Confounding Factors, Epidemiologic; D006801:Humans; D015588:Observer Variation; D015203:Reproducibility of Results; D012106:Research / Q000706:statistics & numerical data*; D012107:Research Design