Table 1.

PICOS (participants, intervention, comparator, outcome, study design) criteria for study selection

Parameter	Criteria
Population	Inclusion criteria: Studies must: (1) be original ones on SFFQ validation processes; (2) analyse nutrient and energy intake, with or without food group analysis, and without an exclusive focus on specific nutrients; (3) include healthy adults as subjects with no special nutritional needs; (4) have study populations composed of elderly individuals without cognitive impairment (in studies conducted on this population subgroup); (5) include analyses with correlation coefficients and (6) be published in either English, Spanish, French or Portuguese. Exclusion criteria: Studies must not: (1) validate SFFQ designed for specific diseases (e.g. cancer) or conditions (e.g. post myocardial infarction); (2) report only food group analyses; (3) present data only in tertiles, quartiles or quintiles without reporting correlation coefficients and (4) include data reported in a previous paper.
Intervention or exposure	Non-applicable
Comparator	Non-applicable
Outcome	Primary outcomes: reference method used for validation of SFFQ, correlation coefficients for energy, nutrients and/or food groups; inclusion of reproducibility analysis, correlation coefficients reported for reproducibility, time frame for reproducibility assessment. SFFQ characteristics (number of items, number of intake frequency response categories, inclusion of visual support, administration method). Secondary outcomes: participant characteristics (sex of participants, age ranges or mean and standard deviation), validation studies characteristics (year of publication, country, region or continent, number of participants).
Study design	Validation studies

SFFQ, semiquantitative FFQ.