Table 2.

Recommendations for validation studies of FFQs measuring sodium intake based on Cade and colleagues9

Food Frequency Questionnaire

FFQs should be validated in population of interest, with reference to regularly updated food composition databases that relate to local food supplies

FFQs should include an estimate of discretionary salt used (in cooking or at the table)

Reference method: 24‐h urine

24‐h urinary sodium excretion is the recommended reference method

At least two and up to seven 24‐h urine collections per participant should be collected

Urine collections should be undertaken over a similar period of assessment as the FFQ

24‐h urine collections should be assessed for completeness using a suitable method (such as PABA excretion)

Statistical analysis

Multiple methods should be used, depending on the purpose of research

Group means should be considered for studies where an assessment of population mean is the outcome of interest

For epidemiological studies, Bland‐Altman methods should be used to assess agreement between sodium estimates from FFQs and urinary excretion

Additional useful statistical methods include correlation, regression, and κ if data are to be presented as categorical or binary

Relative bias should be considered (eg, at high or low intakes or in different population subgroups)

Sample size should be carefully considered–at least 50 to 100 participants–for each population group has been suggested

Reporting

Details of results of validation studies should be reported in utilization studies, rather than describing the FFQ as a “validated questionnaire”

Abbreviations: FFQ, food frequency questionnaire; PABA, para‐amino benzoic acid.