Table 1. Aspects of databases that reflect the quality of data contained within.

Quality Domain	Explanation
Coverage
Representativeness	How well does the data source represent the population that it intends to?
Completeness of recruitment	This feature measures the extent to which all eligible individuals have been included in the data collection scheme
Variables included	What is the extent of the data collected on each individual? Are demographic, exposure, outcome, and confounding variables present?
Completeness of variables	What is the extent of the missing data?
Accuracy
Collection of raw data	Is the raw data collected or are aggregate averages collected?
Explicit definitions	Are the variables explicitly defined?
Explicit rules	Are there explicit rules for deciding how variables are recorded? For example, the timing of physiologic variables.
Reliability of coding	Was the reliability of coded conditions and interventions tested?
Independence of observations	Was the data recorder blinded to patient outcome at the time the data were collected?
Data validation	Were data validated using outside sources? Were there consistency checks?

Based upon Black, et al.(42)