Abstract: Each step about data which are collected, reported and manipulated has an error rate associated with it.Therefore, measuring data quality is a key element of quality control for clinical trial data.The techniques of measuring data quality includes:evaluating data precision, establishing inter-rater reliability, aggregating statistics and statistical process control charts, cross checking between referential data, checking the format of lab reports, checking among relevant documents and data, comparing between source data and CRF, and between CRF and database, data validating, calculating error rate in the processes of data processing, laboratory normalizing and data cleaning.

Key words: quality control, measuring data quality, source document, source data, data precision