摘要
Validity in research is referred to the closeness of the observed results to the truth or the degree to which an inference drawn from a study.1 Guarantee and pursuit of validity is always a challenge through the whole course of a research.What blocks research to reach validity？-Bias.Generally speaking,the more complicate the study is,the larger the bias and the lower the validity are.The cohort study,especially for a prospective cohort study,is a kind of epidemiological study which can provide strong evidences for medical practices and policy-making.
Validity in research is referred to the closeness of the observed results to the truth or the degree to which an inference drawn from a study.1 Guarantee and pursuit of validity is always a challenge through the whole course of a research.What blocks research to reach validity？-Bias.Generally speaking,the more complicate the study is,the larger the bias and the lower the validity are.The cohort study,especially for a prospective cohort study,is a kind of epidemiological study which can provide strong evidences for medical practices and policy-making.
基金
This work was supported by grants from National Natural Science Foundation （No. 81372958） and 973 Program （No. 2012CB316501）.
