Table 1.

Criteria for assessing data quality

Quality level	Criteria
Method for exposure measurement
High	Urinary sodium excretion by 24-hour urine collection and high quality of urine collection
Low	Urine spot test or questionnaire
Unclear	Insufficient information to permit judgement
Method and setting for measurement of outcome
High	Measured multiple times, by trained professional and using standardised procedures. If measured by oscillometric method, the device is clinically validated.
Low	Otherwise (if not all criteria mentioned above are met)
Unclear	Insufficient information to permit judgement
External validity
High	Characteristics of study population are relatively representative of, and generalizable to, the general population
Low	Characteristics of study population are present in only a specific part of the population (eg, hypertensive children, obese children, etc)
Unclear	Insufficient information to permit judgement
Reporting
High	Complete report and if applicable trial registration
Low	Incomplete report (eg, not all prespecific primary outcomes are reported), source of financial support is missing or impartial
Unclear	Insufficient information to permit judgement