Reliability of a Self-Administered Postal Questionnaire on the Use of Food Supplements in an Italian Adult Population

Abstract

The objective of this study was to evaluate the reliability of a self-administered postal questionnaire on the use of food supplements. The study was carried out in subjects representative of an Italian adult population. Eight thousand eight hundred twenty-three subjects received the questionnaire; 1723 subjects completed it of which 102 twice (baseline and 1-month re-administration). The latter 204 questionnaires were used to test reliability using Cohen’s kappa statistic (k) and the intra-class correlation coefficient (ICC) for categorical and quantitative variables, respectively. Subjects’ characteristics such as sociodemographic and physical data, lifestyles, dietary habits, and most health characteristics showed very good agreement (ICC or k 1.00 - 0.55) between questionnaires, with the exception of answers about the consumption of some medicines (k 0.37 - 0.40). The reliability concerning the use of food supplements was satisfactory on the whole (k 0.69) and fairly satisfactory for different categories of food supplements (k 0.83 - 0.41). With regard to additional information about users of food supplements, the reliability of responses was fairly satisfactory on the whole (k 0.93 - 0.41), with some exceptions. The concordance/correlation coefficient values generally showed that the questionnaire is fairly reliable over the entire sample for collecting information on the use of food supplements.

Use of food supplements and determinants of usage in a sample Italian adult population

“…The age brackets used for participants were the same as those used to stratify the population before the selection of the sample (18)(19)(20)(21)(22)(23)(24)(25) (20) . Alcohol consumption was categorized as never/occasionally, #2 glasses/d or .2 glasses/d, on the basis of the Italian Guidelines for Healthy Nutrition (21) , which indicates a moderate consumption of alcohol (,2-3 glasses/d for men and 1-2 glasses/d for women).…”

“…Regarding the information collected relative to behaviours, because the reliability of this section of the questionnaire was not totally satisfactory (19) , we decided to consider these data with caution and not to show them in the current paper.…”

“…The reliability of the questionnaire was tested on a sample of 102 men and women (19) . The data obtained relating to their characteristics, such as sociodemographic and physical data, lifestyle, dietary habits and most health characteristics, showed very good agreement between the two questionnaires (baseline and 1-month re-administration).…”

Screening for Frailty in Older Adults Using a Postal Questionnaire: Rationale, Methods, and Instruments Validation of the INTER‐FRAIL Study

“…A response rate of >50% in people of this age can be considered satisfactory, especially in Italy; as a comparison, 1,723 questionnaires were returned completed out of 8,823 sent out in a recent large Italian survey conducted by mail in younger subjects. 17 The single disability item of the INTER-FRIAL tool efficiently identified persons who should be targeted for supportive care more than for prevention of disability, leaving subjects in whom the yield and the sensitivity of the frailty screening tool were adequate. The screening procedure correctly identified the majority of frail participants, who were possibly amenable to preventive interventions.…”

Dietary Supplement Use among a Population of University Students in Italy: Correlations with BMI, Dietary Habits and Sport Activities

“…Institutional Review Board Approval was not necessary as established by our central academic office. The questionnaire was previously designed and tested by Giammarioli and colleagues [21]. It consisted of three parts.…”